def delete_expired_users(self):
        """
        Checks for expired users and delete's the ``User`` associated with
        it. Skips if the user ``is_staff``.

        :return: A list containing the deleted users.

        """
        deleted_users = []
        for user in get_user_model().objects.filter(is_staff=False,
                                                    is_active=False):
            if user.userena_signup.activation_key_expired():
                deleted_users.append(user)
                user.delete()
        return deleted_users