Revert "code hoisting pass based on GVN"

This reverts commit r274305, since it breaks self-hosting:
  http://lab.llvm.org:8080/green/job/clang-stage1-configure-RA_build/22349/
  http://lab.llvm.org:8011/builders/clang-x86_64-linux-selfhost-modules/builds/17232

Note that the blamelist on lab.llvm.org:8011 is incorrect.  The previous
build was r274299, but somehow r274305 wasn't included in the blamelist:
  http://lab.llvm.org:8011/builders/clang-x86_64-linux-selfhost-modules

llvm-svn: 274320