Remove rocketfuel code, keep a small compatibility layer for the API (bug 1106586, bug 1058292)

https://bugzilla.mozilla.org/show_bug.cgi?id=1106586
https://bugzilla.mozilla.org/show_bug.cgi?id=1058292
No, it works, it'll just leave orphaned translations, but we should have something else to clean them up.