DEPR: remove v018 resample compatibilitiy
closes #20554

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=h1) Report
> Merging [#20782](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8def64931af8a01f4af50d79a8d628fe3e63f00c?src=pr&el=desc) will **decrease** coverage by `0.06%`.
> The diff coverage is `87.5%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20782/graphs/tree.svg?height=150&src=pr&token=eZ4WkYLtcO&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20782      +/-   ##
==========================================
- Coverage   91.84%   91.78%   -0.07%     
==========================================
  Files         153      153              
  Lines       49305    49247      -58     
==========================================
- Hits        45286    45203      -83     
- Misses       4019     4044      +25
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.17% <87.5%> (-0.07%)` | :arrow_down: |
| #single | `41.88% <12.5%> (-0.02%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/20782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.06% <87.5%> (-0.37%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20782/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.2% <0%> (-3.61%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=footer). Last update [8def649...1a8ab25](https://codecov.io/gh/pandas-dev/pandas/pull/20782?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jorisvandenbossche @TomAugspurger if any comments @jorisvandenbossche I don't see a note from you. Perhaps it wasn't submitted?