Remove on-object mailkeys from Phriction
Summary: Depends on D19619. Ref T13065. Ref T13077. Migrate Phriction mail keys to the new infrastructure and drop the column.
Test Plan: Ran migrations, spot-checked the database.
Reviewers: amckinley
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13077, T13065
Differential Revision: https://secure.phabricator.com/D19620