CLN: PY3 compat signature
- [x] xref #25725
- [x] tests passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Replace `compat.signature` for `inspect.getfullargspec`
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=h1) Report
> Merging [#26016](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a1fee9199eba7ebf423880243936b9f1501d3d3a?src=pr&el=desc) will **decrease** coverage by `51.09%`.
> The diff coverage is `25%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26016/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26016      +/-   ##
==========================================
- Coverage   91.82%   40.72%   -51.1%     
==========================================
  Files         175      175              
  Lines       52551    52536      -15     
==========================================
- Hits        48256    21397   -26859     
- Misses       4295    31139   +26844
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `40.72% <25%> (-0.13%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `65.09% <ø> (-10.74%)` | :arrow_down: |
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `69.23% <0%> (-22.2%)` | :arrow_down: |
| [pandas/core/apply.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBwbHkucHk=) | `50.92% <50%> (-47.69%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/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/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.16%)` | :arrow_down: |
| ... and [133 more](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26016?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/26016?src=pr&el=footer). Last update [a1fee91...60aca53](https://codecov.io/gh/pandas-dev/pandas/pull/26016?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/26016?src=pr&el=h1) Report
> Merging [#26016](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a1fee9199eba7ebf423880243936b9f1501d3d3a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `80%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26016/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26016      +/-   ##
==========================================
- Coverage   91.82%   91.82%   -0.01%     
==========================================
  Files         175      175              
  Lines       52551    52536      -15     
==========================================
- Hits        48256    48239      -17     
- Misses       4295     4297       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.38% <80%> (ø)` | :arrow_up: |
| #single | `40.72% <20%> (-0.13%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `74.52% <ø> (-1.31%)` | :arrow_down: |
| [pandas/core/apply.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBwbHkucHk=) | `98.61% <100%> (ø)` | :arrow_up: |
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `91.34% <66.66%> (-0.09%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26016/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/26016/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26016?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/26016?src=pr&el=footer). Last update [a1fee91...49749f8](https://codecov.io/gh/pandas-dev/pandas/pull/26016?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @mroeschke 