A fix for swatches that can't be deleted!
This answer is taken from the Adobe User to User Forum - it seems a little strange, but it does work. It would be ideal if Adobe would address this issue:
1. Create a new document
2. In that document, create a process color but give it the same name as the spot color that you want to remove.
3. Make a book consisting only of the two documents.
4. Synchronize the documents (in the bookpalet)
5. Now you will be able to delete the color from the swatches pallet of the previously relunctant file.
It's a pretty quick fix.