Bug 982029 - [MMS/SMS] Display email in SMS/MMS Threads r=Julien

https://bugzilla.mozilla.org/show_bug.cgi?id=982029
you dont need all this, because the 'equals' filter already does this. This is needed in the `findExact` function (which is really `findExactByName`) because the contacts API can't match the full name and instead we need to match separately firstName and lastName.
I think it's enough to just do `return this.findBy({ ... }, callback)`.