Remove outputs in on_train_epoch_end hooks

[carmocca]

What does this PR do?

Follow-up to the deprecation in #7339

Does your PR introduce any breaking changes? If yes, please list them.

The removal of outputs argument after the deprecation

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[codecov]

Codecov Report

Merging #8587 (b6569fc) into master (6b47cbe) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #8587    +/-   ##
=======================================
- Coverage      92%     88%    -4%     
=======================================
  Files         218     218            
  Lines       14398   14364    -34     
=======================================
- Hits        13296   12669   -627     
- Misses       1102    1695   +593     

[tchaton]

LGTM !