Provide a more flexible script for administrative management of audits

Summary: Fixes T3679. This comes up every so often and the old script is extremely broad (nuke everything in a repository). Provide a more surgical tool.

Test Plan: Ran a bunch of variations of the script and they all seemed to work OK.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, staticshock

Maniphest Tasks: T3679

Differential Revision: https://secure.phabricator.com/D6678