Fixes T6637, "closing by commit" should update task status and specify responsible commit, but drop the artificial comment.

Summary: When updating the status of a task via commit, transaction should show responsible commit and status update if it was changed.

Test Plan: Push a commit "Fixes Txx", transaction should include status update and commit number.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6637

Differential Revision: https://secure.phabricator.com/D11230