R1:6ed123e0801a

Propagate "unexpandable" PHIDs to feed notification recipient expansion

Summary:
See PHI466. Ref T13108. Somewhat recently, new rules were added so that "Resigning" from a revision takes you off the default recipient list, even if you're still a member of a project or package that is still a reviewer or subscriber.

However, these rules don't currently apply to the similar expansion which occurs in notifications. If you resign from a revision you may still get some notifications (just not email) if a…