Update to latest multi-db - still receive update notification

I'm sure I'm doing something wrong, but I do not know what.
I just replaced the db.php with the latest one. Probably it is not enough as the notification is still there for multi-db

btw I do not think we need the multi-db plugin in the plugins directory, do we? Is it serving any purpose?
I believe db.php and db-config are the only one needed for running in multi-db mode