CLN: remove unused TimeGrouper._get_binner_for_resample() method
 - [x] tests passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [ ] whatsnew entry

method seems unused and is not covered by tests -> remove it?

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=h1) Report
> Merging [#16152](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3b80ed33e00957fec4a79cde19df66d809b5d3a7?src=pr&el=desc) will **increase** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16152/graphs/tree.svg?src=pr&width=650&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16152      +/-   ##
==========================================
+ Coverage   90.83%   90.85%   +0.01%     
==========================================
  Files         159      159              
  Lines       50796    50785      -11     
==========================================
  Hits        46143    46143              
+ Misses       4653     4642      -11
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.64% <ø> (+0.01%)` | :arrow_up: |
| #single | `40.32% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.06% <ø> (+1.6%)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16152?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/16152?src=pr&el=footer). Last update [3b80ed3...465e555](https://codecov.io/gh/pandas-dev/pandas/pull/16152?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks, don't remember fully what I added this. this was replaced by ``_get_binner`` which dispatched to the correct subclass.