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.

llvm-svn: 147719