Returns True if students can unregister from course

def allow_unregister(self, plugin_override=True):
        """ Returns True if students can unregister from course """
        vals = self._hook_manager.call_hook('course_allow_unregister', course=self, default=self._allow_unregister)
        return vals[0] if len(vals) and plugin_override else self._allow_unregister