Simplify track grad norm condition

[carmocca]

What does this PR do?

Part of #9287

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

None, track_grad_norm == -1 is the default value (inactive). Passing 0 will result in an error after #9765.

can_log is already checked inside the LoggerConnector

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[codecov]

Codecov Report

Merging #9992 (26938f8) into master (a99b744) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #9992    +/-   ##
=======================================
- Coverage      93%     89%    -4%     
=======================================
  Files         179     179            
  Lines       15805   15803     -2     
=======================================
- Hits        14630   14022   -608     
- Misses       1175    1781   +606