Herald - make dry runs work for "apply once" rules after they have been applied
Summary: Fixes T3719
Test Plan: https://secure.phabricator.com/T3719#comment-7
Reviewers: epriestley
Reviewed By: epriestley
CC: Korvin, aran
Maniphest Tasks: T3719
Differential Revision: https://secure.phabricator.com/D6968