Core/PetAI: apply some movement related corrections

Unit::StopMoving() is evil, and so is MotionMaster::Clear()

the first can really mess up existing movement generators
the second can interrupt "controlled" movements... can do it literally mid-air

src/server/game/AI/CoreAI/PetAI.cpp

@@ -449,7 +449,6 @@ void PetAI::MovementInform(uint32 type, uint32 id)
             {
                 ClearCharmInfoFlags();
                 me->GetCharmInfo()->SetIsAtStay(true);
-                me->GetMotionMaster()->Clear();
                 me->GetMotionMaster()->MoveIdle();
             }
             break;