Revert "add tests for bugs fixed by the GVN hoist pass"

This reverts commit r274327 since the tests fail.  E.g.:
  http://lab.llvm.org:8011/builders/clang-x86_64-linux-selfhost-modules/builds/17240

It looks like this commit is building on r274305, but that commit caused
a miscompile and was reverted in r274320.

llvm-svn: 274332