r/samba-dc: sysvolsync: Use system DNS server

Forcing the PDC lookup to use localhost as the DNS server does not work
when first adding a new domain controller, as the `sysvolsync` script
runs before Samba starts.  There isn't much advantage to using the local
DNS server over the system-defined server anyway.

roles/samba-dc/files/sysvolsync.sh

@@ -23,7 +23,7 @@ info() {
 }
 
 get_pdc() {
-    dig @localhost +short -t srv _ldap._tcp.pdc._msdcs.$(dnsdomainname) \
+    dig +short -t srv _ldap._tcp.pdc._msdcs.$(dnsdomainname) \
         | sort -n \
         | awk '{print $4;exit}'
 }