Set update-checking to false by default.

This is an obsoleted feature.

inc/config.php

@@ -40,7 +40,7 @@
     $config['blotter'] = &$config['global_message'];
 
     // Automatically check if a newer version of Tinyboard is available when an administrator logs in.
-    $config['check_updates'] = true;
+    $config['check_updates'] = false;
     // How often to check for updates
     $config['check_updates_time'] = 43200; // 12 hours