Hide the "added a commit/revision" stories from feed and mail

Summary:
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.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13276

Differential Revision: https://secure.phabricator.com/D20491