Revert "[DAG] Fold shuffle(bop(shuffle(x,y),shuffle(z,w)),bop(shuffle(a,b),shuffle(c,d)))"

This reverts commit 5dfba562.

That commit causes an assertion failure with the following repro:

typedef long b __attribute__((__vector_size__(16)));
b *d;
b e;
b __attribute__((__always_inline__)) c(b h, b i) {
  return (__attribute__((__vector_size__(8 * sizeof(short)))) short)h + i;
}
j() {
  b k, l, m, n, o[6], p, q;
  m = d[5];
  b r = m;
  b s = f(r, 8);
  q = s;
  l = d[1];
  p = l;
  t(q);
  n = c(m, l);
  o[1] = c(s, f(p, 8));
  k = __builtin_shufflevector(n, o[1], 0, 2);
  e = __builtin_ia32_psrlwi128(k, j);
}

./bin/clang -cc1 -triple x86_64-grtev4-linux-gnu -emit-obj -O1 -std=c99 test.c