You're right...Add/Remove is missing from TweakUI since Win 2K. Why? I don't know. Ask M$.
You have to open "regedit", and navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Uninstall
You have to click one-by-one on keys in left pane, until you'll find an entry you want to remove, in right pane.
Then, right click on found entry, and click "Delete".