Continue replacing Commit/Audit status checks with object-based checks

Summary: Ref T13195. See PHI851. Continuing down the path toward replacing these legacy numeric constants with more modern string constants.

Test Plan:

• Raised concern, requested verification, verified.
• Looked at commit hovercard with audit status.
• Viewed header on a commit page.
• (Didn't test the Doorkeeper stuff since it requires linking to Asana and seems unlikely to break.)

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13195

Differential Revision: https://secure.phabricator.com/D19647