docs: def strip(self):
          """Remove rollbacks, rollforwards, and all non-current files.
  
          When distributing a refpkg, you probably want to distribute as
          small a one as possible.  strip removes everything from the
          refpkg which is not relevant to its current state.
          """
          self._sync_from_disk()
          current_filenames = set(self.contents['files'].values())
          all_filenames = set(os.listdir(self.path))
          to_delete = all_filenames.difference(current_filenames)
          to_delete.discard('CONTENTS.json')
          for f in to_delete:
              self._delete_file(f)
          self.contents['rollback'] = None
          self.contents['rollforward'] = None
          self.contents['log'].insert(
              0, 'Stripped refpkg (removed %d files)' % len(to_delete))
          self._sync_to_disk()