horribly fix plain-text email for modular transactions

Summary:
This is the quickest and dirtiest fix I could come up with.

PhabricatorApplicationTransaction::getTitleForMail() is using clone $this, which doesn't actually effect implementation.
Ref T9789.

Test Plan: update paste comment, get plaintext mail.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley

Maniphest Tasks: T9789

Differential Revision: https://secure.phabricator.com/D16251