CLN: Old timezone issues
- [x] closes #21846
- [x] closes #21737
- [x] closes #20724
- [x] closes #18785
- [x] closes #18308 
- [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/22201?src=pr&el=h1) Report
> Merging [#22201](https://codecov.io/gh/pandas-dev/pandas/pull/22201?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/776fed3ab63d74ddef6e5af1a702b10c2a30bbb6?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/22201/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/22201?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22201   +/-   ##
=======================================
  Coverage   92.06%   92.06%           
=======================================
  Files         169      169           
  Lines       50694    50694           
=======================================
  Hits        46671    46671           
  Misses       4023     4023
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.47% <ø> (ø)` | :arrow_up: |
| #single | `42.32% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22201?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/22201?src=pr&el=footer). Last update [776fed3...f0c125d](https://codecov.io/gh/pandas-dev/pandas/pull/22201?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @mroeschke nice cleaning these old issues!