Port the code to PHP 8.5.

Replace the short open tags and the removed functions (mcrypt, mysql_error,
salt-less crypt). Decode the reCAPTCHA reply as JSON, turn off mysqli
exceptions, drop stripslashes(), and default missing input values.
Fix the misplaced continue in prune_images().

google.inc.php

@@ -1,4 +1,4 @@
-<?
+<?php
 $ga_id = config('GOOGLE_ANALYTICS_ID');
 if (! $is_admin && $ga_id) { ?>
 <script>
@@ -10,4 +10,4 @@ if (! $is_admin && $ga_id) { ?>
   ga('create', <?= json_encode($ga_id, JSON_HEX_TAG) ?>, 'auto');
   ga('send', 'pageview');
 </script>
-<? } ?>
+<?php } ?>