Apply diffusion.createcomment directly with transaction editor in Audit

Summary: Ref T4896. Use the new transaction-oriented PhabricatorAuditEditor directly instead of invoking it via the old editor.

Test Plan: Used Conduit to add a comment, use silent mode, and accept a commit.

Reviewers: joshuaspence, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4896

Differential Revision: https://secure.phabricator.com/D10126