[X86][SSE] foldShuffleOfHorizOp - remove broadcast handling.

Remove VBROADCAST/MOVDDUP/splat-shuffle handling from foldShuffleOfHorizOp

This can all be handled by canonicalizeShuffleMaskWithHorizOp along as we check that the HADD/SUB are only used once (to prevent infinite loops on slow-horizop targets which will try to reuse the nodes again followed by a post-hop shuffle).