Replace old commit edit controller with new EditEngine controller

Summary: Ref T10978. The new controller now does everything the old one did, so swap 'em and nuke the old one.

Test Plan: Edited a commit, hit the new controller, things worked real good.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10978

Differential Revision: https://secure.phabricator.com/D17177