Support DestructionEngine in MetaMTAMail
- It causes us to write a destruction log, which is slightly silly (we're deleting one thing and creating another).
- It's a little bit slower than not using DestructionEngine.
However, it gets us some stuff for free that's likely relevant now (e.g., Herald Transcript cleanup) and I'm planning to move attachments to Files, but want to be able to delete them when mail is destroyed.
The destruction log is a touch silly, but those records are very small and that log gets GC'd later without generating new logs. We could silence the log from the GC if it's ever an issue.
Test Plan: Used bin/remove destroy and bin/garbage collect --collector mail.sent to destroy mail and collect garbage.
Reviewed By: amckinley
Maniphest Tasks: T13053
Differential Revision: https://secure.phabricator.com/D18985