Revert "[LoopUnswitch] Fix incorrect Modified status"

This reverts commit dfd447c2.

After I pushed this commit, llvm-sphinx-docs started failing, due to:

  Warning, treated as error:
  extension 'recommonmark' has no setup() function;
  is it really a Sphinx extension module?

I don't see how this commit may have caused that, but I'm still
reverting it since I don't know how to proceed with that
troubleshooting.