TST/CLN: Old timezone issues PT3
- [x] closes #13783
- [x] closes #12619
- [x] closes #15522
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

xref #21612 and #21491, last of the cleanup of older timezone issues

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21674?src=pr&el=h1) Report
> Merging [#21674](https://codecov.io/gh/pandas-dev/pandas/pull/21674?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/dc45fbafef172e357cb5decdeab22de67160f5b7?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/21674/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21674?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21674   +/-   ##
=======================================
  Coverage    91.9%    91.9%           
=======================================
  Files         154      154           
  Lines       49657    49657           
=======================================
  Hits        45638    45638           
  Misses       4019     4019
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.28% <ø> (ø)` | :arrow_up: |
| #single | `41.9% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21674?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/21674?src=pr&el=footer). Last update [dc45fba...4b1f818](https://codecov.io/gh/pandas-dev/pandas/pull/21674?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @mroeschke 