I believe this come from our upstream docker image, at this line
https://github.com/discourse/discourse_docker/blob/master/image/base/Dockerfile#L3
That line points to the official Ubuntu image from the Docker library which has this line:
https://github.com/tianon/docker-brew-ubuntu-core/blob/dist-amd64/xenial/Dockerfile#L2
where it adds this archive that contains the restricted lines you found.
I don’t know if there is an official Ubuntu docker image with those disabled.