Remove CI jobs for Debian oldoldstable.

"oldoldstable" is two releases behind the current stable release. It's not supported by upstream so we should not build for it either.

And the CI builds for "wheezy" broke today when "oldoldstable"'s repo was moved from deb.debian.org to archive.debian.org as announced at https://lists.debian.org/debian-devel-announce/2019/03/msg00006.html

The container images at https://hub.docker.com/_/debian and https://github.com/debuerreotype/docker-debian-artifacts/blob/3e751c2c2f60037e9231ed94bbd1f95347af2c87/oldoldstable/slim/Dockerfile have not yet caught up with the new repo location.