Remove getmxrr alias dns_get_mx test

The test is currently failing, and the same functionality is
already tested (in a better way) in the getmxrr() test.

ext/standard/tests/network/dns_get_mx.phpt

@@ -1,27 +0,0 @@
---TEST--
-bool dns_get_mx ( string $hostname , array &$mxhosts [, array &$weight ] );
---CREDITS--
-marcosptf - <marcosptf@yahoo.com.br> - @phpsp - sao paulo - br
---SKIPIF--
-<?php
-if (getenv("SKIP_SLOW_TESTS"))
-    die("skip slow test");
-if (getenv("SKIP_ONLINE_TESTS"))
-    die("skip test requiring internet connection");
-if (substr(PHP_OS, 0, 3) == 'WIN') {
-    die('skip: no Windows support');
-}
-?>
---FILE--
-<?php
-$domains = array('php.net', 'doc.php.net', 'wiki.php.net');
-foreach ($domains as $domain) {
-    if (getmxrr($domain, $hosts, $weights)) {
-        echo "Hosts: " . count($hosts) . ", weights: " . count($weights) . "\n";
-    }
-}
-?>
---EXPECTF--
-Hosts: %i, weights: %i
-Hosts: %i, weights: %i
-Hosts: %i, weights: %i