Because I love shiny new things, I enrolled in the macOS Sierra public beta to play around with it before its general release. Once Sierra was released, I no longer wanted to receive public beta updates. In the past, I’ve gone to System Preferences -> App Store and disabled beta updates. Normally, this would remove the updates from appearing in the App Store’s Software Updates, however, this time I was still getting notified of new public betas. That’s when I found this thread on Apple’s forums. The solution, opening up Terminal and typing the following command:
sudo softwareupdate --clear-catalog
Running the command removed the beta updates from the App Store and now all is right with the world. I thought I’d post this solution in case anyone else runs into this issue as well.