Revert "[MachineCopyPropagation] Extend pass to do COPY source forwarding" round 2

This reverts commit r311135.

sanitizer-x86_64-linux-android buildbot is timing out with just this
patch applied.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311142 91177308-0d34-0410-b5e6-96231b3b80d8
77 files changed