I pushed a commit to Github with some private information. I've created a new branch that no longer has that information, and I've deleted the old branch, so the commit doesn't show up in the history of the branches.
However, you can still access a Github page showing the old commit using a URL in this format: https://github.com/me/myrepo/commit/4d929e07c2a61f261950f37af8d6fe5ec5ed05e1#diff-84e94b10bf89d08c7eb37dc4887fc612fb3115ff806e2661eb9e07c2a6186ebeR1. The commit in question does not show up if you run git log.
How can I get rid of it?