bug#16928: 24.3.50; file _flymake not deleted on remote hosts

[Leo Liu]

1. emacs -q
2. (add-hook 'find-file-hook 'flymake-find-file-hook)
3. make sure the php executable is available
4. save https://github.com/drupal/drupal/raw/7.x/update.php in a remote
   host
5. open it in emacs

And I see update_flymake.php not being deleted (cleaned up). So it seems
at the time flymake-simple-cleanup was called, (file-exists-p
"/host:/path/to/update_flymake.php") returned false.

This is kinda annoying because after a while I see lots of _flymake*
files in the project.

Leo