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

This reverts commit r311038.

Several buildbots are breaking, and at least one appears to be due to
the forwarding of physical regs enabled by this change.  Reverting while
I investigate further.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311062 91177308-0d34-0410-b5e6-96231b3b80d8
89 files changed