[plt-scheme] uninstalling .plt packages in 299

Matthew Flatt wrote:

>Ok, I see a bug. If no collections (other than "info-domain") are left
>in a collection root, then the info-domain cache is not updated.
>
>Is that what you're seeing?
>  
>
Is the intended behavior that info-domain files should always be rebuilt 
every time the user runs setup-plt? If that's the case, I can fix it to 
do that, I was just editing setup-unit.ss to deal with PLaneT stuff 
recently so it's current in my head.

-jacob