Revert "Re-enable "[MachineCopyPropagation] Extend pass to do COPY source forwarding""

This reverts commit r314729.

Another bug has been encountered in an out-of-tree target reported by Quentin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314814 91177308-0d34-0410-b5e6-96231b3b80d8
90 files changed