lb_http: use http_server_simple_response()
lb_http: use http_server_simple_response()

Obeys the http_status_is_empty() rule, and avoids assertion failures
and HTTP protocol errors.

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy