How to hide “You are now logged out” message on WordPress login form?

Solution: 

Yes hii interesting, perhaps it might be useful to override the error ID loggedout:

add_filter('wp_login_errors', 'my_logout_message');

function my_logout_message($errors) {
    // Remove the message

    $errors->remove('loggedout');

    // Or customize the message:

    if (array_key_exists('loggedout', $errors->errors)) {
        $errors->errors['loggedout'][0] = 'My message';
    }

    return $errors;
}