MetaMTA - make sure mail garbage collection also cleans up recipient edges
Summary: Ref T5791. This edge table grows 2+X faster than the corresponding mail table depending on usage. Ergo, lets make sure to clean that up too in the delete code.
Test Plan: careful thought
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T5791
Differential Revision: https://secure.phabricator.com/D13408