I believe we can remove this wakelock code (and above) from compose.js with the changes to the back-end.  We'll only be holding the wi-fi wake-lock for as long as it takes the backend to enqueue the operation.  While there might be arguments for holding a cpu wake-lock to prevent us suddenly being suspended before that gets enqueued, etc., it seems like those should happen at the MailAPI level of abstraction, not here (where this was a hack to workaround the lack of wakelocks in the backend).