Remove unnecessary columns for all dataset types in `Trainer`
Author: Yard1
Pull request: yes

# What does this PR do?

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As discussed with @sgugger offline, this PR adds automatic removal of unnecessary columns for arbitrary dataset types. This mimics the already present logic for removing unnecessary columns from `datasets.Dataset`s, but uses a wrapper around the data collation function to enable it for other datasets. The end result is intended to be the same for both cases.

The implementation is a bit more complex than it really has to be, in order to facilitate the same logging UX as with the `datasets.Dataset` case.

Tests have been added/updated where applicable.

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Comments:
cc @sgugger 

_The documentation is not available anymore as the PR was closed or merged._

Ah, yeah, we don't need to check whether it's an iterable dataset! Let me fix that