Removing unused 8.x-1.x branch

The Password Policy module ( has an unused 8.x-1.x branch with a single commit deleting all 7.x-1.x files. The actual D8 version of the module is in the 8.x-3.x branch.

I am trying to delete the 8.x-1.x branch because it is unused and a nuisance. (People mistakenly submit issues against it.) But:

 $ git push origin :8.x-1.x
Enter passphrase for key '/home/aohrvetpv/.ssh/id_rsa': 
remote: The branch '8.x-1.x' is identified as an official development branch on, and therefore cannot be deleted.

Is there a way I can remove it? If not, could someone possibly remove it for us?