When i use this, I didn't show warning.
I don't know if it's right way.
But, It's doesn't show warning
/public_html/config/settings.inc.php
define('MCRYPT_RIJNDAEL_128','0');
define('_RIJNDAEL_KEY_', '5pgGJ2HeBq6cKGAMmnvpeWgIXfiOkmfe');
define('_RIJNDAEL_IV_', '/gcs9WXANrjXXpp406hwrg==');