The answer today is to email me privately with the link to delete. Assuming no one else has guessed and loaded the URL, that might be fine for mitigation of a unimportant unwanted file being shared.
I deleted the snippet you mentioned. But as Matt said, you posted this link to a public mailing list, so you will need to do whatever is appropriate to account for the fact that whatever secret was there was publicly findable for a few hours and is no longer secret.
We should probably have a note somewhere on the playground answering this question, since this is the second time it's happened in the past few months. I created
golang.org/issue/18530 for that.
Russ