refactor(stdlibs): remove dropped 3.8 mapping

[mkniewallner]

Follow-up to #874.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.5%. Comparing base (9f7391f) to head (57bc80b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #910   +/-   ##
=====================================
  Coverage   92.5%   92.5%           
=====================================
  Files         37      37           
  Lines       1006    1006           
  Branches      99      99           
=====================================
  Hits         931     931           
  Misses        60      60           
  Partials      15      15           

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