remove obsoleted parts of setup/dns.sh

Now that dns_update is a part of the management daemon, we no
longer are using STORAGE_ROOT/dns for anything.

setup/dns.sh

 # DNS: Configure a DNS server using nsd
 #######################################
 
-# After running this script, you also must run setup/dns_update.sh,
-# and any time a zone file is added/changed/removed, and any time a
-# new domain name becomes in use by a mail user.
-#
-# This script will turn on DNS for $PUBLIC_HOSTNAME.
+# This script installs packages, but the DNS zone files are only
+# created by the /dns/update API in the management server because
+# the set of zones (domains) hosted by the server depends on the
+# mail users & aliases created by the user later.
 
 source setup/functions.sh # load our functions
 
@@ -20,26 +19,13 @@ else
 	useradd nsd;
 fi
 
-# Okay now install the package.
+# Okay now install the packages.
 
 apt_install nsd
 
 # Prepare nsd's configuration.
 
 sudo mkdir -p /var/run/nsd
-mkdir -p "$STORAGE_ROOT/dns";
-
-# Create the default zone if it doesn't exist.
-
-if [ ! -f "$STORAGE_ROOT/dns/$PUBLIC_HOSTNAME.txt" ]; then
-	# can be an empty file, defaults are applied elsewhere
-	cat > "$STORAGE_ROOT/dns/$PUBLIC_HOSTNAME.txt" << EOF;
-EOF
-fi
-
-# Let the storage user own all DNS configuration files.
-
-chown -R $STORAGE_USER.$STORAGE_USER $STORAGE_ROOT/dns
 
 # Permit DNS queries on TCP/UDP in the firewall.