Revert "RegScavenging: Add scavengeRegisterBackwards()"

Reverting this commit for now as it seems to be causing failures on
test-suite tests on the clang-ppc64le-linux-lnt bot.

This reverts commit r276044.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276068 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed