Revert "Make APIEditBeforeSave give the whole revision"

Revert "Make APIEditBeforeSave give the whole revision"

This may negatively affect performance and the whole purpose of the
hook (making it possible to reject an edit from an extension while
providing detailed error information in the API result) has been
invalidated by 09a5febb7b024c0b6585141bb05cba13a642f3eb, which lets
EditFilterMergedContent do this too.

I think it was intentional that the hook was called with just the text
passed to action=edit API. Making it actually be called with the text
that's going to be saved would require more work (e.g. for
automatically resolved edit conflicts, T73947).

Very few extensions use this hook. I'm fixing AbuseFilter to use
EditFilterMergedContent in I30c1e3d0a6c10888e6ac53745313434474663cce,
we should also review ConfirmEdit, ProofreadPage and SpamBlacklist to
see what behavior they really expect.

This reverts commit be97167ab61e7d59d86f6a9dca53b7016d615735.

Change-Id: I62713419496bcf57364a8fa9de93c0c8ddc3e91c