Ref T2543. This cleans up a couple of remaining rough edges:

• We could do an older TYPE_ACTION "close" via the daemons.
• We could do an older TYPE_ACTION "close" via arc close-revision, explicitly or implicitly in arc land, via API (differential.close).
• We could do an older TYPE_ACTION "rethink" ("Plan Changes") via the API, via arc diff --plan-changes (differential.createcomment).

Move these to modern modular transactions, then get rid of all the validation and application logic for them. This nukes a bunch of ArcanistDifferentialRevision::... junk.

• Used bin/repository reparse --message rXYZ... to reparse a commit, closing a corresponding revision.
• Used differential.close to close a revision.
• Used differential.createcomment to plan changes to a revision.
• Reviewed transaction log for full "closed by commit" message (linking to commit and mentioning author).
• Grepped for ::TYPE_ACTION to look for remaining callsites, didn't find any.
• Grepped for differential.close and differential.createcomment in arcanist/ to look for anything suspicious, seemed clean.