Audit Feed: less verbose when the author is the committer

Summary:
If the author and the committer are the same person, do not show them twice.

From:

UsernameFoo committed <commit hash>: <commit msg> (authored by UsernameFoo).

To:

UsernameFoo committed <commit hash>: <commit msg>

This only affects the feed.

Before	After

Closes T15528

Test Plan: Do some mixed commits and visit /feed/query/all/. No nuclear implosions.

Reviewers: O1 Blessed Committers, speck

Reviewed By: O1 Blessed Committers, speck

Subscribers: speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15528

Differential Revision: https://we.phorge.it/D25421