Remove check for alternative port from Goss test

Since version 4.6.0, coturn no longer listens on an alternative port if
config option `no-rfc5780` is set (which is the default and recommended).

See these upstream commits for details:
coturn/coturn@eda1169
coturn/coturn@54ef051

templates/test_coturn.yml.j2

@@ -5,13 +5,9 @@ port:
 {% if coturn_tls %}
   tcp:{{ coturn_tls_listening_port }}:
     listening: true
-  tcp:{{ coturn_listening_port|int + 1 }}:
-    listening: true
 {% endif %}
   udp:{{ coturn_listening_port }}:
     listening: true
-  udp:{{ coturn_listening_port|int + 1 }}:
-    listening: true
 service:
   coturn:
     enabled: true