CLN: deprecate the pandas.tseries.plotting.tsplot function (GH18627)
- [X] closes #18627 
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19980?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@aedbd94`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `0%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19980/graphs/tree.svg?height=150&token=eZ4WkYLtcO&width=650&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19980?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #19980   +/-   ##
=========================================
  Coverage          ?   91.64%           
=========================================
  Files             ?      150           
  Lines             ?    49051           
  Branches          ?        0           
=========================================
  Hits              ?    44954           
  Misses            ?     4097           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.02% <0%> (?)` | |
| #single | `41.79% <0%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19980?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_timeseries.py](https://codecov.io/gh/pandas-dev/pandas/pull/19980/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL190aW1lc2VyaWVzLnB5) | `60.2% <0%> (ø)` | |

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[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19980?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/19980?src=pr&el=footer). Last update [aedbd94...dc70e9b](https://codecov.io/gh/pandas-dev/pandas/pull/19980?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jorisvandenbossche - I've gone ahead and made the rewording changes (TimeSeries -> Series) you've requested and squashed everything together for cleanliness. Thanks a lot!

> and squashed everything together for cleanliness.

For future reference, you don't need to bother doing that. We squash everything on merging the PR anyway, and keeping the multiple commits makes it easier what was updated after a review.