Re-enable upstream behaviour of systemd-tmpfiles --purge
    
    From the 257 release notes:
    
    * The --purge switch of systemd-tmpfiles (which was added in v256) has
      been reworked: it will now only apply to tmpfiles.d/ lines marked
      with the new "$" flag. This is an incompatible change, and means any
      tmpfiles.d/ files which shall be used together with --purge need to
      be updated accordingly. This change has been made to make it harder
      to accidentally delete too many files when using --purge incorrectly.
    
    The feature is now sufficiently hard to misuse that we can drop the patch.