Remove Python 2 in CLASSIFIERS

[gfyoung]

Follow-up to #26330 (comment)

@WillAyd

[codecov]

Codecov Report

Merging #26339 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26339      +/-   ##
==========================================
+ Coverage   92.04%   92.04%   +<.01%     
==========================================
  Files         175      175              
  Lines       52289    52292       +3     
==========================================
+ Hits        48130    48133       +3     
  Misses       4159     4159

Flag	Coverage Δ
#multiple	90.59% <ø> (-0.01%)	⬇️
#single	40.88% <ø> (+0.02%)	⬆️

Impacted Files	Coverage Δ
pandas/core/dtypes/dtypes.py	96.42% <0%> (-0.24%)	⬇️
pandas/core/dtypes/base.py	100% <0%> (ø)	⬆️
pandas/core/internals/blocks.py	94.07% <0%> (ø)	⬆️
pandas/core/dtypes/cast.py	91.54% <0%> (ø)	⬆️
pandas/core/arrays/integer.py	96.35% <0%> (+0.02%)	⬆️
pandas/util/testing.py	90.7% <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 4e4f5bd...c2637d7. Read the comment docs.

[codecov]

Codecov Report

Merging #26339 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26339      +/-   ##
==========================================
+ Coverage   92.04%   92.04%   +<.01%     
==========================================
  Files         175      175              
  Lines       52289    52289              
==========================================
+ Hits        48130    48131       +1     
+ Misses       4159     4158       -1

Flag	Coverage Δ
#multiple	90.59% <ø> (ø)	⬆️
#single	40.87% <ø> (+0.01%)	⬆️

Impacted Files	Coverage Δ
pandas/util/testing.py	90.7% <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 4e4f5bd...c2637d7. Read the comment docs.