Delete "Post Published. View Post" for custom post type

I’m working on a plugin with a custom post type called "important_dates"

I want to delete the WordPress admin notification when a new custom post is created.

Here is my code – it deletes the notifications for all post types. How do I make it work for only my "important_dates" custom post type?

add_filter( 'post_updated_messages', 'post_published' );

function post_published( $messages )
{
    unset($messages['posts'][6]);
    return $messages;
}
}