Remove unnecessary generic Callback class

[lebrice]

Signed-off-by: Fabrice Normandin normandf@mila.quebec

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.78261% with 7 lines in your changes missing coverage. Please review.

Project coverage is 81.59%. Comparing base (b40ef22) to head (7245443).

Files with missing lines	Patch %	Lines
project/algorithms/callbacks/samples_per_second.py	87.09%	4 Missing ⚠️
...ect/algorithms/callbacks/classification_metrics.py	84.61%	2 Missing ⚠️
project/algorithms/jax_ppo_test.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #94      +/-   ##
==========================================
- Coverage   81.71%   81.59%   -0.13%     
==========================================
  Files          59       58       -1     
  Lines        4064     4026      -38     
==========================================
- Hits         3321     3285      -36     
+ Misses        743      741       -2     

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