Apparently, you can’t. But there’s no real need to either, I have similar devices on my system on the Sonos DB. Fortunately, when updating to S2, it only looks at devices that are currently in use.

The only way I’m aware of to get them removed is to have them added to someone else’s account, which requires a factory reset on your side of the device, and then someone adding it to their system, which triggers the removal from your account. 

But my BRIDGE which as recycled when I replaced it with a BOOST still sits there, mocking me. Fortunately, I only looked at that page four or five times when the upgrade announcement was made. I’ve not looked at it since. 

You can’t. But even if you could, it wouldn’t have any effect on anything at all.