Prune deprecated trainer attributes

[Borda]

What does this PR do?

remove deprecated trainer attributes such as use_* or on_*

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[codecov]

Codecov Report

Merging #7501 (7cb1816) into master (9698109) will decrease coverage by 0%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7501    +/-   ##
=======================================
- Coverage      92%     92%    -0%     
=======================================
  Files         198     198            
  Lines       12927   12843    -84     
=======================================
- Hits        11945   11823   -122     
- Misses        982    1020    +38     

[ananthsub]

more tests need to be cleaned up to reflect the removed properties

re-review