Move those declarations out of the action. Simply paste both of them in the functions.php file and it will work (tested).
wp_deregister_script('wp-mediaelement');
wp_deregister_style('wp-mediaelement');
Move those declarations out of the action. Simply paste both of them in the functions.php file and it will work (tested).
wp_deregister_script('wp-mediaelement');
wp_deregister_style('wp-mediaelement');