CLN: minor cleanups for MultiIndex.codes
Minor cleanup for #23752. The whatsnew didn't parse properly and other small stuff.
Hello @topper-123! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/indexes/frozen.py`](https://github.com/topper-123/pandas/blob/185b780001acc3bbae20f9f522edebe719a442e0/pandas/core/indexes/frozen.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=h1) Report
> Merging [#24146](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f492be63d7e904c2e0fa8113a72b761ee4b74219?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/24146/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24146   +/-   ##
=======================================
  Coverage    92.2%    92.2%           
=======================================
  Files         162      162           
  Lines       51700    51700           
=======================================
  Hits        47670    47670           
  Misses       4030     4030
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.6% <ø> (ø)` | :arrow_up: |
| #single | `43.02% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/frozen.py](https://codecov.io/gh/pandas-dev/pandas/pull/24146/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9mcm96ZW4ucHk=) | `92.1% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24146?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/24146?src=pr&el=footer). Last update [f492be6...185b780](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=h1) Report
> Merging [#24146](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f492be63d7e904c2e0fa8113a72b761ee4b74219?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/24146/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24146   +/-   ##
=======================================
  Coverage    92.2%    92.2%           
=======================================
  Files         162      162           
  Lines       51700    51700           
=======================================
  Hits        47670    47670           
  Misses       4030     4030
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.6% <ø> (ø)` | :arrow_up: |
| #single | `43.02% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/frozen.py](https://codecov.io/gh/pandas-dev/pandas/pull/24146/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9mcm96ZW4ucHk=) | `92.1% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24146?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/24146?src=pr&el=footer). Last update [f492be6...185b780](https://codecov.io/gh/pandas-dev/pandas/pull/24146?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks! i think some more things need changing

see earnings : 
https://travis-ci.org/pandas-dev/pandas/jobs/467305227