Remove pandas.io.formats.css from MyPy Blacklist

[WillAyd]

There was a seemingly unused class variable which was failing mypy due to a lack of annotation. On closer inspection however it doesn't appear that this was even used, so I figured deletion makes things simpler.

I suppose if this was subclassed it could have some effect but this isn't part of the exposed API

@jnothman if you have any thoughts or objections

[jnothman]

I suppose it doesn't have much use here, for now at least... Don't mind.

[codecov]

Codecov Report

Merging #25900 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #25900      +/-   ##
==========================================
+ Coverage   91.53%   91.53%   +<.01%     
==========================================
  Files         175      175              
  Lines       52808    52807       -1     
==========================================
  Hits        48338    48338              
+ Misses       4470     4469       -1

Flag	Coverage Δ
#multiple	90.09% <100%> (-0.01%)	⬇️
#single	41.82% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/formats/excel.py	97.4% <100%> (ø)	⬆️
pandas/io/formats/css.py	100% <100%> (ø)	⬆️
pandas/util/testing.py	90.56% <0%> (+0.1%)	⬆️

---

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[codecov]

Codecov Report

Merging #25900 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #25900      +/-   ##
==========================================
+ Coverage   91.53%   91.53%   +<.01%     
==========================================
  Files         175      175              
  Lines       52808    52807       -1     
==========================================
  Hits        48338    48338              
+ Misses       4470     4469       -1

Flag	Coverage Δ
#multiple	90.09% <100%> (-0.01%)	⬇️
#single	41.82% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/formats/excel.py	97.4% <100%> (ø)	⬆️
pandas/io/formats/css.py	100% <100%> (ø)	⬆️
pandas/util/testing.py	90.56% <0%> (+0.1%)	⬆️

---

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 882961d...80f0523. Read the comment docs.

[jreback]

thanks @WillAyd