That doesn't do anything.
Cheekeez, I think I found the answer. Let me know if it works for you (for my future reference as well)!
Click Manage Account and login. Under Devices you should see "Playstation Systems." Click that and you can view all the systems associated with your account. Click on the system you wish to deactivate, which will take you to another screen. You should see "Deactivate" in the Device Type row.
Hope that works!