CLN: minor cleanups for MultiIndex.codes

[topper-123]

Minor cleanup for #23752. The whatsnew didn't parse properly and other small stuff.

[pep8speaks]

Hello @topper-123! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/indexes/frozen.py !

[codecov]

Codecov Report

Merging #24146 into master will not change coverage.
The diff coverage is n/a.

@@           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)	⬆️
#single	43.02% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/indexes/frozen.py	92.1% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f492be6...185b780. Read the comment docs.

[codecov]

Codecov Report

Merging #24146 into master will not change coverage.
The diff coverage is n/a.

@@           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)	⬆️
#single	43.02% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/indexes/frozen.py	92.1% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f492be6...185b780. Read the comment docs.

[jorisvandenbossche]

Thanks!

[jreback]

i think some more things need changing

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