'Removes a U2F device but never removes the last one.  This returns
False if the last device would be removed.'

def remove_u2f_device(self, key):

    devices = [x for x in (self.config.get('devices') or ()) if (x['binding']['keyHandle'] != key)]
    if devices:
        self.config['devices'] = devices
        return True
    return False
