proxmox: only install firewall rules on one node

And let the cluster take care of distribution.

roles/proxmox/tasks/user.yml

@@ -1,7 +1,5 @@
+# synchronize user and group data from LDAP when sync-ldap context key is set to a realm
 - block:
-    - set_fact:
-        primary: '{{ nodes | map(attribute="inventory_hostname") | sort | first }}'
-
     - name: Install LDAP sync script
       template:
         dest: /usr/local/bin/sync-ldap.py