remove deprecated early_stop_callback

[Borda]

What does this PR do?

remove deprecated early_stop_callback

PR review

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[codecov]

Codecov Report

Merging #3982 into master will decrease coverage by 2%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #3982    +/-   ##
=======================================
- Coverage      89%     87%    -2%     
=======================================
  Files         216     216            
  Lines       15569   15600    +31     
=======================================
- Hits        13870   13619   -251     
- Misses       1699    1981   +282     

[rohitgr7]

Why is it removed BTW?

[awaelchli]

@rohitgr7 because the 1) we can't guess the monitor key to use for early stopping, it is better for the user to explicitly set it. 2) there should be only one way to pass in callbacks (via callbacks arg)

[rohitgr7]

@awaelchli what about ModelCheckpoint? It's a callback too right?

[awaelchli]

yes, but Lightning does checkpoints by default, and if we removed that argument then there would be no way to turn checkpointing off (i.e. checkpoint_callback=None)

[chrismaliszewski]

So, should one pass ModelCheckpoint inside callbacks or still via checkpoint_callback?

[awaelchli]

sorry, missed your question.
Via callbacks list is the preferred way for all callbacks. Passing ModelCheckpoint in to callbacks "should" already work on the latest master branch. However there are some edge cases we need to sort out with this usecase. I am currently looking into this.
I personally recommend still using checkpoint_callback until ~v1.1.