Remove tab by third party from all repositories/organizations

I have also asked this at SO here, and found some help, but I am still experiencing this issue.

I have a third party app “ZenHub” that I no longer want to use. I have removed it under Settings > Application > Authorized OAuth apps, but the tab is stil visible in all my personal and organizational repositories. I also get a “Sign in to ZenHub” notification in the bottom right corner of my repositories.

One at SO suggested that I go into the repository’s settings, and remove the tab under custom tabs, but I do not have this setting. I did find a ZenHub connection under the setting webhooks. This temporarily removed the ZenHub tab for that repository only, but the tab is now back.

I would like to have these removed. I have pictures showing the Zenhub tab below (since I am a new user, I cannot additionally post a picture of the notification).