API: Drop DataFrame.iterkv()
Deprecated since 0.17.0

xref #10711

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15650?src=pr&el=h1) Report
> Merging [#15650](https://codecov.io/gh/pandas-dev/pandas/pull/15650?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.


```diff
@@            Coverage Diff             @@
##           master   #15650      +/-   ##
==========================================
- Coverage   91.01%   90.99%   -0.03%     
==========================================
  Files         143      143              
  Lines       49379    49376       -3     
==========================================
- Hits        44943    44929      -14     
- Misses       4436     4447      +11
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15650?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/compare/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30...e40fc9e64e260e95228c9ae2465d9d0506e0aa04?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.24% <ø> (-0.01%)` | :x: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/compare/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30...e40fc9e64e260e95228c9ae2465d9d0506e0aa04?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :x: |
| [pandas/tools/merge.py](https://codecov.io/gh/pandas-dev/pandas/compare/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30...e40fc9e64e260e95228c9ae2465d9d0506e0aa04?src=pr&el=tree#diff-cGFuZGFzL3Rvb2xzL21lcmdlLnB5) | `91.76% <0%> (-0.35%)` | :x: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/compare/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30...e40fc9e64e260e95228c9ae2465d9d0506e0aa04?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.87% <0%> (-0.1%)` | :x: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15650?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/15650?src=pr&el=footer). Last update [15e8e9a...e40fc9e](https://codecov.io/gh/pandas-dev/pandas/compare/15e8e9a53d036f8e436ae5ad4eff66fc48f67d30...e40fc9e64e260e95228c9ae2465d9d0506e0aa04?src=pr&el=footer&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). thanks! keep em coming! (any 0.17.0 removals are of course fair game)