R1:50f4adef64cf

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