check for container name not empty is not needed

https://github.com/docker/docker/blob/e379e2668cecf8a0f9ef29eb57ee881f4d313d58/api/server/server.go#L356

https://github.com/docker/docker/blob/master/api/server/server.go#L863

Check is not needed because the http handler didn't match that route with an empty string
