[X86][SNB] Fix differences between vex/non-vex XMM vector moves (PR37286)

As confirmed by llvm-exegesis, there is no scheduler difference between MOVDQA/MOVDQU and VMOVDQA/VMOVDQU xmm reg-reg moves

Another chapter in the never ending crusade to remove useless InstRW overrides from the x86 scheduler models......

llvm-svn: 333271