Remove most of the legacy hunk code
Summary: Ref T8475. This gets rid of most of the old "legacy hunk" code. I'll nuke the rest (and drop the old table) once we're more sure that we're in the clear.
Test Plan: Browsed Differential.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T8475
Differential Revision: https://secure.phabricator.com/D17040