Simplify Prometheus listen_address details

doc/administration/monitoring/prometheus/index.md

@@ -59,8 +59,8 @@ Although possible, it's not recommended to change the port Prometheus listens
 on, as this might affect or conflict with other services running on the GitLab
 server. Proceed at your own risk.
 
-To access Prometheus from outside the GitLab server, set an FQDN or IP in
-`prometheus['listen_address']`. To change the address/port that Prometheus
+To access Prometheus from outside the GitLab server,
+change the address/port that Prometheus
 listens on:
 
 1. Edit `/etc/gitlab/gitlab.rb`