Moves FANGS mouthgear check

Muzzles used to block mouthgear so there wasn't any point in checking for it if you had a muzzle.  With the XL mouthgear, that's no longer the case, so pulled the check into general from the no-muzzle option and deleted the reference to MUZZLE_BEAR since that doesn't affect the chance to bite.

(Haven't compiled this one locally yet.  No reason it shouldn't work, but just in case...)