Revert "ValueMapper: Make LocalAsMetadata match function-local Values"

This reverts commit r265631, since it caused bot failures:
http://lab.llvm.org:8011/builders/clang-ppc64be-linux/builds/3256
http://lab.llvm.org:8011/builders/clang-cmake-aarch64-42vma/builds/7272

Looks like something is depending on the old behaviour.  I'll try to
track it down and recommit.

llvm-svn: 265637