restrict public interface of training loop

[awaelchli]

What does this PR do?

All methods that are not part of the public interface get special protection from agent underscore.

• Adds an underscore ( _ ) before pretty much any method and attribute. It looks ugly but you have to get used to it.
• Remove a small piece of dead code
• No other changes

Part of #7938

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Did you have fun?

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[pep8speaks]

Hello @awaelchli! Thanks for updating this PR.

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

Comment last updated at 2021-06-23 10:00:02 UTC

[codecov]

Codecov Report

Merging #8024 (ccccf15) into master (a45ab00) will decrease coverage by 0%.
The diff coverage is 98%.

@@          Coverage Diff           @@
##           master   #8024   +/-   ##
======================================
- Coverage      92%     92%   -0%     
======================================
  Files         211     211           
  Lines       13669   13655   -14     
======================================
- Hits        12538   12496   -42     
- Misses       1131    1159   +28