Delete deprecated TrainerTrainingTricksMixin

[carmocca]

What does this PR do?

See title

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

Removes deprecated code

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[codecov]

Codecov Report

Merging #8679 (fdec9c0) into master (850416f) will increase coverage by 4%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #8679    +/-   ##
=======================================
+ Coverage      88%     93%    +4%     
=======================================
  Files         168     167     -1     
  Lines       13985   13964    -21     
=======================================
+ Hits        12355   12929   +574     
+ Misses       1630    1035   -595