Remove commit list from Diffusion in favor of Audit commit list

Summary:
We can drive this query better from the Audit tool now; get rid of the Diffusion
version.

Preserve usernames in URIs as per T900.

Test Plan: Clicked "Commits" from profile. Browsed audit commit filters.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T904

Differential Revision: https://secure.phabricator.com/D1713