dbscripts: nginx: remove unnecessary unique filter

The intention of "unique" in "groups['buildservers'] | sort | unique"
was to account for combining multiple groups and passing them to the
sort and unique filters. However, with only one group it looks silly.

roles/dbscripts/templates/nginx.d.conf.j2

@@ -25,7 +25,7 @@ server {
         satisfy any;
         auth_request /devel/mirrorauth/;
 
-{% for host in groups['buildservers'] | sort | unique %}
+{% for host in groups['buildservers'] | sort %}
         # {{ host }}
 {% for address in ['ipv4_address', 'ipv6_address'] if address in hostvars[host] %}
         allow {{ hostvars[host][address] }};