req: remove void requirements after bump to py3.9+

[Borda]

What does this PR do?

removing requirements that are not valid since we bumped min python version to 3.9

Before submitting

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2917.org.readthedocs.build/en/2917/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69%. Comparing base (5fc2e0b) to head (95ac383).

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2917   +/-   ##
======================================
  Coverage      69%     69%           
======================================
  Files         346     346           
  Lines       19172   19172           
======================================
  Hits        13236   13236           
  Misses       5936    5936