CLN/DEPR: removed deprecated as_indexer arg from str.match()
- [x] closes #22316 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

removed as_indexer(deprecated of 0.20.0) arg completely from str.match. 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22356?src=pr&el=h1) Report
> Merging [#22356](https://codecov.io/gh/pandas-dev/pandas/pull/22356?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cf70d11a25ec59a5b630921d86759c7fa49884db?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22356/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/22356?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22356      +/-   ##
==========================================
- Coverage   92.05%   92.05%   -0.01%     
==========================================
  Files         169      169              
  Lines       50709    50705       -4     
==========================================
- Hits        46679    46675       -4     
  Misses       4030     4030
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <100%> (-0.01%)` | :arrow_down: |
| #single | `42.26% <66.66%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22356?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/22356/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.62% <100%> (-0.01%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22356?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/22356?src=pr&el=footer). Last update [cf70d11...b109d19](https://codecov.io/gh/pandas-dev/pandas/pull/22356?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 see my comment: https://github.com/pandas-dev/pandas/issues/22316#issuecomment-413499326

I am not sure we can remove this for 0.24.0 @jreback What do you suggest as the next course of action on this issue? can you rebase Pull request moved to #22626