[X86] Remove ANY_EXTEND special case from canReduceVMulWidth

[X86] Remove ANY_EXTEND special case from canReduceVMulWidth

Removing this code doesn't affect any lit tests so it doesn't appear to be tested anymore. I assume it was when it was added, but I guess something else changed? Code coverage report also says its unused.

I mostly didn't like that it seemed to count the sign bits as if it was a sign_extend, but then set isPositive as if it was a zero_extend. It feels like we should have picked one interpretation?

Differential Revision: https://reviews.llvm.org/D54596

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346995 91177308-0d34-0410-b5e6-96231b3b80d8