How can I get rid of the notification that a Mac App store app which is not installed on this machine wants to update
One simple way to stop this would be to go ahead with the update and let it do what it wants to do. If it installs the app you can then remove it. The app could be in a different folder than applications. Have you tried searching for the app name using Spotlight search or a Finder Search? The update button in the App Store just says it thinks the app is on your machine.