When you visited our Demo site or set up your own site you granted Overdrive permission to access certain areas of your Google account. If you wish to remove these permissions you can do so from your Google Account by visiting:
https://myaccount.google.com/permissions
...where you'll see a list of Apps you have connected to your Google account, click on Overdrive and choose "Remove".

To remove Overdrive from Google Drive:

• From the settings menu, select Manage apps.
• Find the app in the list and click the Options button.
• Select Remove this app or Disconnect from Drive.

See also Deleting your Overdrive Site.