Remove deprecated on_{save,load}_checkpoint signature

[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 #8697 (392fcf7) into master (0aa5cc7) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #8697   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         172     172           
  Lines       14114   14097   -17     
======================================
- Hits        13094   13077   -17     
  Misses       1020    1020