Revert part of r147716. Looks like x87 instructions kill markers are all messed

Revert part of r147716. Looks like x87 instructions kill markers are all messed
up so branch folding pass can't use the scavenger. :-(  This doesn't breaks
anything currently. It just means targets which do not carefully update kill
markers cannot run post-ra scheduler (not new, it has always been the case).

We should fix this at some point since it's really hacky.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147719 91177308-0d34-0410-b5e6-96231b3b80d8