Hide the "added a commit/revision" stories from feed and mail
Ref T13276. Previously, these edges were added directly with an EdgeEditor, so they did not generate transaction stories.
Now, they're added properly, but they aren't terribly useful in feed/mail. Hide them in those contexts, like we already do with other types of similar edges.
Test Plan: Will verify behavior on secure.
Reviewed By: amckinley
Maniphest Tasks: T13276
Differential Revision: https://secure.phabricator.com/D20491