make is to when a user resigns from an audit they are no longer cc'd

Summary: do this by making sure to filter out those who've "resigned" from the email CC list

Test Plan: resigned from an audit and no longer got emails on updates

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2033

Differential Revision: https://secure.phabricator.com/D3890