That's pretty much what I was trying to say... you can decline to add more license to your own work, and decline to ask for your own attribution, but you can't erase the underlying license and WTFPL the whole thing, as the only license.
See here: https://creativecommons.org/licenses/by/3.0/
> If supplied, you must provide the name of the creator and attribution parties, a copyright notice, a license notice, a disclaimer notice, and a link to the material.
For reference, here is how official Golang README puts it:
> The Go gopher was designed by Renee French. (http://reneefrench.blogspot.com/)