In reply to Craig Finch.

support@github.com says you're supposed to remove infringing material from your entire history using the process described here: https://help.github.com/articles/remove-sensitive-data. Though, if you're forking a repo that is already on GitHub I highly doubt that anyone is going to be angry at you for not removing stuff that was already in the history.

And in this case, content that I added was never on GitHub before. The fork was of an older publically available version of the plugin, which I then added the non-publically available updates to.