BLD: use setup.cfg's version

[Zeroto521]

• closes #xxxx
• whatsnew entry

To drop setup.py.

[codecov]

Codecov Report

Merging #441 (7b228c1) into main (d292bdf) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #441   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files          23       23           
  Lines         549      549           
  Branches       73       73           
=======================================
  Hits          548      548           
  Partials        1        1           

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