Remove evaluation loop legacy dict returns for *_epoch_end hooks

[ananthsub]

What does this PR do?

Split out from #6969

This seems like it's been deprecated since v0.9.1 and doesn't change the behavior.

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[codecov]

Codecov Report

Merging #6973 (f7a0679) into master (80c5293) will decrease coverage by 5%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #6973    +/-   ##
=======================================
- Coverage      92%     87%    -5%     
=======================================
  Files         194     194            
  Lines       12366   12326    -40     
=======================================
- Hits        11350   10669   -681     
- Misses       1016    1657   +641     

[carmocca]

Looks like we had a test checking this warning message

[ananthsub]

thanks for the additional cleanup @carmocca !

[ethanwharris]

LGTM 😃

[tchaton]

LGTM ! Thanks.