It was only a matter of time before this happened.
Impulse was supposed to be used to uninstalll everything, then reinstalled through the store or the new SDC. Numerous posts have been made concerning this. If that is now not possible, I think you'll need to contact support on this one.
It may be possible to use a recent restore point to go back before the Gamestop update, run Impulse while offline and uninstall everything.
Good luck.
Edit: If you follow Frankief's advice, make sure you run Impulse offline or it will autoupdate you right back where you started.
