No need to mirror these images if we don't use them anymore.
Remove debian 8 and 9, and ubuntu zesty. The latter is the codename for
ubuntu 17.04, which is a non-LTS and was unsupported since 2018-01-13.
Related: OS#5601
Change-Id: If1c198038b0fd5faf0763172447962969448940e
Follow up on the change of using almalinux instead of centos8 in
docker-playground, with providing the almalinux base images in the
Osmocom registry.
Related: SYS#5818
Related: docker-playground I30e1a773b901b1d2187214445116c7f2aecc4e36
Change-Id: I93a8892da628b8d2f9cbb2a6453e8ab3153a9c4a
Oliver Smith
Harald Welte