CLN: Removing find_undoc_args.py, validate_docstrings.py implements the same
The script `find_undoc_args.py` was used to detect functions that the documented parameters did not match the signature ones.

`validate_docstrings.py` implements the same validation, among many more. So the script is not needed anymore.

sure merge away # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=h1) Report
> Merging [#24693](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d56db9d6a20b063ce27b6e8c898f0d3b5db2e175?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24693/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24693   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files         166      166           
  Lines       52310    52310           
=======================================
  Hits        48326    48326           
  Misses       3984     3984
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (ø)` | :arrow_up: |
| #single | `43.06% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24693?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/24693?src=pr&el=footer). Last update [d56db9d...5125107](https://codecov.io/gh/pandas-dev/pandas/pull/24693?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/24693?src=pr&el=h1) Report
> Merging [#24693](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d56db9d6a20b063ce27b6e8c898f0d3b5db2e175?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24693/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24693   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files         166      166           
  Lines       52310    52310           
=======================================
  Hits        48326    48326           
  Misses       3984     3984
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (ø)` | :arrow_up: |
| #single | `43.06% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24693?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/24693?src=pr&el=footer). Last update [d56db9d...5125107](https://codecov.io/gh/pandas-dev/pandas/pull/24693?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
