Remove check_checkpoint_callback

[carmocca]

What does this PR do?

Changes:

• Replace training_loop.on_train_end call to check_checkpoint_callback with the on_train_end hook implementation in ModelCheckpoint
• Always rely on the ModelCheckpoint hooks to save.

This resolves a bug where an extra checkpoint was saved at the end of training if the val_check_interval did not align with the training batches. In that case, a checkpoint was always saved as if save_last was set to True even if it was not. This change is reflected in the tests.

Fixes #6672

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[pep8speaks]

Hello @carmocca! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-07-19 10:52:34 UTC

[codecov]

Codecov Report

Merging #7724 (6ad0a5e) into master (999ef5c) will decrease coverage by 5%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7724    +/-   ##
=======================================
- Coverage      93%     88%    -5%     
=======================================
  Files         217     217            
  Lines       14227   14218     -9     
=======================================
- Hits        13201   12530   -671     
- Misses       1026    1688   +662     

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[tchaton]

LGTM !