Revert "Make OrderedInstructions and OrderedBasicBlock use AssertingVH, to try and catch mistakes"

This reverts commit 50ec560f05dcb8a1be18be442660d0305bc7de25.

It catches some bug in NewGVN it seems. I am in middle of something and will not be able to investigate
Revert for now.

http://lab.llvm.org:8011/builders/clang-atom-d525-fedora-rel/builds/6268

llvm-svn: 306608