Attempts to remove the blacklisted directories from `directories`
        and then returns whatever is left in the set.

        Called from the `collect_directories` method.

def _remove_blacklisted(self, directories):
        """
        Attempts to remove the blacklisted directories from `directories`
        and then returns whatever is left in the set.

        Called from the `collect_directories` method.
        """
        directories = util.to_absolute_paths(directories)
        directories = util.remove_from_set(directories,
                                           self.blacklisted_directories)

        return directories