CLN: Remove unnecessary code

[suminb]

frozenset() and frozenset([]) essentially produce identical results, and thus there is no need to pass an empty list to create an empty frozenset.

• tests added / passed (CI is still running...)
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry (no new feature)

[pep8speaks]

Hello @suminb! Thanks for submitting the PR.

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

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

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

• In the file pandas/tests/dtypes/test_inference.py, following are the PEP8 issues :

Line 62:18: E241 multiple spaces after ','

[jreback]

ok sure

[codecov]

Codecov Report

Merging #23696 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #23696      +/-   ##
==========================================
+ Coverage   92.24%   92.24%   +<.01%     
==========================================
  Files         161      161              
  Lines       51318    51340      +22     
==========================================
+ Hits        47339    47361      +22     
  Misses       3979     3979

Flag	Coverage Δ
#multiple	90.64% <100%> (ø)	⬆️
#single	42.34% <100%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
pandas/core/groupby/groupby.py	96.51% <100%> (ø)	⬆️
pandas/core/accessor.py	98.79% <100%> (ø)	⬆️
pandas/core/generic.py	96.82% <100%> (ø)	⬆️
pandas/core/indexes/datetimelike.py	97.74% <0%> (-0.28%)	⬇️
pandas/tseries/offsets.py	96.98% <0%> (-0.09%)	⬇️
pandas/core/arrays/period.py	98.44% <0%> (-0.05%)	⬇️
pandas/core/indexes/datetimes.py	96.11% <0%> (-0.01%)	⬇️
pandas/core/arrays/datetimes.py	98.47% <0%> (+0.03%)	⬆️
pandas/core/arrays/datetimelike.py	96.14% <0%> (+0.21%)	⬆️
pandas/core/dtypes/concat.py	96.66% <0%> (+0.4%)	⬆️
... and 1 more

---

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[jbrockmendel]

Is the noqa still needed?

[jreback]

yes, this has to do with liniing things up.

[jreback]

thanks @suminb