drop unused variable in API

[Borda]

What does this PR do?

dropping some unused arguments from APIP which does not affect user

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

Anyone in the community is free to review the PR once the tests have passed.
Before you start reviewing make sure you have read Review guidelines. In short, see the following bullet-list:

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

Merging #6308 (6c190a5) into master (ac58378) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #6308   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         160     160           
  Lines       11399   11398    -1     
======================================
- Hits        10640   10610   -30     
- Misses        759     788   +29     

[Borda]

not sure how much this makes sense since the model is not used...
cc: @tchaton

[tchaton]

Yes, it is used in save_model_fn as trainer will access lightning_module. So we re-create full model only temporary. But your changes should be fine.

[carmocca]

The changes here to rpc and ModelCheckpoint are also in #6136. I'd rather get that merged first since it's a P0

[tchaton]

LGTM !

[akihironitta]

Could we remove pl_module from the following private methods, too?:
https://github.com/PyTorchLightning/pytorch-lightning/blob/424b71e145125a0c68ae1c56b3bd4c20d71cee85/pytorch_lightning/callbacks/model_checkpoint.py#L541
https://github.com/PyTorchLightning/pytorch-lightning/blob/424b71e145125a0c68ae1c56b3bd4c20d71cee85/pytorch_lightning/callbacks/model_checkpoint.py#L520

Also, there are still outdated comments # Todo: required argument pl_module is not used in the file model_checkpoint.py.