This one is simple, but I couldn’t find a decent google result for it.
Before you uninstall the plugin, you have to get its name … go to the vendors directory in your app folder and get the name of the folder
In this case the name of the plugin is “active_scaffold”
Go to the directory of the app you want the plugin removed from and type in
ruby script/plugin remove active_scaffold
or if you’re on a Linux box
./script/plugin remove active scaffold