Fix phpmailer-lite bug

Summary: Fixes T4417. In this particular codepath, the lovely CreateHeader already added the to: information, so no need to slap it on the front all ghetto style.

Test Plan: imma push this live and test (I am lazy and don't want to configure amazon ses)

Reviewers: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4417

Differential Revision: https://secure.phabricator.com/D8288