'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.'

def delete_expired_users(self):

    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
