CLN: Address MulitIndex Test Follow Ups in Issue #21918
- [x] closes #21918
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry - N/A

Addresses most of the issues.  Left blowing away the old pickles for another issue which is still open.  
also merged #21900 so will need to rebase # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=h1) Report
> Merging [#21928](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2f2876b8c7ec259d7310a33da2412b07b1850421?src=pr&el=desc) will **increase** coverage by `0.03%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21928/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21928      +/-   ##
==========================================
+ Coverage   91.96%   91.99%   +0.03%     
==========================================
  Files         166      167       +1     
  Lines       50323    50578     +255     
==========================================
+ Hits        46281    46531     +250     
- Misses       4042     4047       +5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.4% <ø> (+0.03%)` | :arrow_up: |
| #single | `42.17% <ø> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `96.11% <0%> (-0.37%)` | :arrow_down: |
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `94.12% <0%> (-0.19%)` | :arrow_down: |
| [pandas/core/arrays/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3BlcmlvZC5weQ==) | `91.18% <0%> (-0.17%)` | :arrow_down: |
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.39% <0%> (-0.14%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `92.08% <0%> (-0.12%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.12% <0%> (-0.05%)` | :arrow_down: |
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `97.34% <0%> (-0.02%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.1% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/dtypes/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbmNhdC5weQ==) | `99.18% <0%> (ø)` | :arrow_up: |
| [pandas/tseries/frequencies.py](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvZnJlcXVlbmNpZXMucHk=) | `95.9% <0%> (ø)` | :arrow_up: |
| ... and [28 more](https://codecov.io/gh/pandas-dev/pandas/pull/21928/diff?src=pr&el=tree-more) | |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=footer). Last update [2f2876b...e993d4d](https://codecov.io/gh/pandas-dev/pandas/pull/21928?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback all green.  @jreback all green.  I made the additional edits and some further cleaning as well.  Thanks! thanks @elmq0022 nice cleaning!