CLN: remove compat.itervalues
- [x] xref #25725

Removes ``compat.itervalues``.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=h1) Report
> Merging [#26099](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7b3bf2dc6b8b00133d2cf46c1f70f2865666a13f?src=pr&el=desc) will **decrease** coverage by `51.22%`.
> The diff coverage is `37.5%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26099/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #26099       +/-   ##
===========================================
- Coverage   91.96%   40.73%   -51.23%     
===========================================
  Files         175      175               
  Lines       52412    52406        -6     
===========================================
- Hits        48199    21346    -26853     
- Misses       4213    31060    +26847
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `40.73% <37.5%> (-0.15%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `81.13% <ø> (-11.6%)` | :arrow_down: |
| [pandas/core/dtypes/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbmNhdC5weQ==) | `51.96% <ø> (-44.63%)` | :arrow_down: |
| [pandas/core/groupby/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9nZW5lcmljLnB5) | `13.3% <0%> (-73.79%)` | :arrow_down: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `33.93% <0%> (-64.28%)` | :arrow_down: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `16.21% <0%> (-19.32%)` | :arrow_down: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `25.86% <100%> (-69.99%)` | :arrow_down: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `31.39% <100%> (-62.45%)` | :arrow_down: |
| [pandas/io/json/normalize.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vbm9ybWFsaXplLnB5) | `8.16% <50%> (-88.78%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| ... and [138 more](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=footer). Last update [7b3bf2d...1168f8f](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=h1) Report
> Merging [#26099](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7b3bf2dc6b8b00133d2cf46c1f70f2865666a13f?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `87.5%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26099/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26099      +/-   ##
==========================================
- Coverage   91.96%   91.95%   -0.01%     
==========================================
  Files         175      175              
  Lines       52412    52405       -7     
==========================================
- Hits        48200    48189      -11     
- Misses       4212     4216       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.51% <87.5%> (-0.01%)` | :arrow_down: |
| #single | `40.72% <37.5%> (-0.15%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `92.45% <ø> (-0.28%)` | :arrow_down: |
| [pandas/core/dtypes/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbmNhdC5weQ==) | `96.56% <ø> (-0.02%)` | :arrow_down: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `35.43% <0%> (-0.1%)` | :arrow_down: |
| [pandas/io/json/normalize.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vbm9ybWFsaXplLnB5) | `96.93% <100%> (ø)` | :arrow_up: |
| [pandas/core/groupby/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9nZW5lcmljLnB5) | `87.07% <100%> (-0.02%)` | :arrow_down: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `98.2% <100%> (-0.01%)` | :arrow_down: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.84% <100%> (ø)` | :arrow_up: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `93.82% <100%> (-0.02%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26099/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.9% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=footer). Last update [7b3bf2d...1168f8f](https://codecov.io/gh/pandas-dev/pandas/pull/26099?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 The failure is the one mentioned by @mroeschke here: https://github.com/pandas-dev/pandas/pull/26081#pullrequestreview-226404142. It's unrelated to this PR. Thanks @topper-123! 