Modernize commit/edge transaction when parsing commit messages
Summary: Ref T5245. With work elsewhere (notably, D9839) we can remove this TODO and use real transactions.
Test Plan: Pushed a closes Txxx commit and got a close + transaction.
Reviewers: chad, btrahan, joshuaspence
Reviewed By: joshuaspence
Subscribers: epriestley
Maniphest Tasks: T5245
Differential Revision: https://secure.phabricator.com/D9848