Remove on_train_batch_{start,end}(dataloader_idx=...)

[carmocca]

What does this PR do?

Part of #12521

#12769 missed these

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

Removes support for the deprecated argument

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cc @Borda @carmocca @awaelchli @ninginthecloud @daniellepintz @rohitgr7