remove xmpp from rest api config

An error log appeared in `/var/log/jitsi/jvb.log` when xmpp was used:

```
2020-04-08 15:58:14.603 SEVERE: [59] ComponentMain.lambda$getConnectCallable$0#293: host-unknown, host:localhost, port:5347
```

It might be due to a misconfiguration of prosody: https://community.jitsi.org/t/ask-xmpp-websocket-configuration/30386/4

As we do not use this, we remove xmpp for rest api config.

roles/common/tasks/jitsi_stats.yml

@@ -6,7 +6,7 @@
     path: "/etc/jitsi/videobridge/sip-communicator.properties"
     regexp: "^org.jitsi.videobridge.ENABLE_STATISTICS"
     line: "org.jitsi.videobridge.ENABLE_STATISTICS=true"
-    
+
 - name: configuration du videobridge pour transporter les stats via colibri REST api
   lineinfile:
     path: "/etc/jitsi/videobridge/sip-communicator.properties"
@@ -23,4 +23,4 @@
   lineinfile:
     path: "/etc/jitsi/videobridge/config"
     regexp: "^JVB_OPTS="
-    line: 'JVB_OPTS=" --apis=rest,xmpp "'
+    line: 'JVB_OPTS=" --apis=rest "'