Drop dependency on pywin32

[kevin-bates]

This dependency should have been dropped as part of the work for #382.

Resolves #281

[codecov-commenter]

Codecov Report

Merging #514 (d9272f2) into master (627898f) will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #514      +/-   ##
==========================================
+ Coverage   77.06%   77.14%   +0.08%     
==========================================
  Files         107      107              
  Lines        9495     9495              
  Branches     1027     1027              
==========================================
+ Hits         7317     7325       +8     
+ Misses       1808     1803       -5     
+ Partials      370      367       -3     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/handlers.py	62.96% <0.00%> (+1.58%)	⬆️
jupyter_server/tests/services/kernels/test_api.py	99.01% <0.00%> (+1.96%)	⬆️

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[SylvainCorlay]

This is great news. Happy to see this dropped. We should be careful about removing it in the conda recipe when it is updated.