remove more dead code

dns/dns.api.inc

-<?php
-
-/**
- * copy of frontend's hosting_dns_split_url
- */
-function _dns_split_url($url) {
-  $tlds = split("\n", variable_get('hosting_dns_tlds', ''));
-  $first_dot = strpos($url, '.');
-
-  # Strip off the first part
-  $host = substr($url, 0, $first_dot);
-  $zone = substr($url, $first_dot);
-
-  # If the remaining hostname is a TLD
-  if (in_array($zone, $tlds)) {
-    # Add the first part back, and that's the zone (the host is @)
-    $zone = $host . $zone;
-    $host = '@';
-  } else {
-    # that's the zone (and the host is the first part)
-    $zone = substr($zone, 1); # strip the leading .
-  }
-
-  return array('host' => $host, 'zone' => $zone);
-}