Make "bin/audit delete" synchronize commit audit status, and improve "bin/audit synchronize" documentation

Summary:
Depends on D20126. See PHI1056. Ref T13244.

• bin/audit delete destroys audit requests, but does not update the overall audit state for associated commits. For example, if you destroy all audit requests for a commit, it does not move to "No Audit Required".
• bin/audit synchronize does this synchronize step, but is poorly documented.

Make bin/audit delete synchronize affected commits.

Document bin/audit synchronize better.

There's some reasonable argument that bin/audit synchronize perhaps shouldn't exist, but it does let you recover from an accidentally (or intentionally) mangled database state. For now, let it live.

Test Plan:

• Ran bin/audit delete, saw audits destroyed and affected commits synchornized.
• Ran bin/audit synchronize, saw behavior unchanged.
• Ran bin/audit help, got better help.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13244

Differential Revision: https://secure.phabricator.com/D20127