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

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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 70%. Comparing base (767c678) to head (a954328).
Report is 8 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #2917    +/-   ##
=======================================
+ Coverage      69%     70%    +1%     
=======================================
  Files         346     346            
  Lines       19172   19172            
=======================================
+ Hits        13236   13428   +192     
+ Misses       5936    5744   -192