FoundationStone currently does not use the Windows "Add/Remove" Control Panel.
Removing it is trivial: delete C:\Program Files\FoundationStone 4.0\, and remove the Fonts you installed (if any). No registry settings were adjusted during the original installation process.
If you like, you can also remove the Sun JRE using the familiar "Add/Remove" Control Panel, but as that is used in your web browser to run Java content, you probably will want to keep it anyway.