Revert "[X86] Canonicalize fp zero vectors from bitcasted integer zero vectors"

This reverts commit 169db80e.

This change is causing many test failures on Windows bots:
- https://lab.llvm.org/buildbot/#/builders/235/builds/3616
- https://lab.llvm.org/buildbot/#/builders/233/builds/4883
- https://lab.llvm.org/buildbot/#/builders/216/builds/31174