Remove a user from a group.

        :type group_name: string
        :param group_name: The name of the group

        :type user_name: string
        :param user_name: The user to remove from the group.

def remove_user_from_group(self, group_name, user_name):
        """
        Remove a user from a group.

        :type group_name: string
        :param group_name: The name of the group

        :type user_name: string
        :param user_name: The user to remove from the group.

        """
        params = {'GroupName' : group_name,
                  'UserName' : user_name}
        return self.get_response('RemoveUserFromGroup', params)