jobs/registry-update-base-images: drop old images

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

jobs/registry-update-base-images.yml

@@ -17,14 +17,10 @@
       - shell: |
           REGISTRY="registry.osmocom.org"
           IMAGES="
-            debian:jessie
-            debian:stretch
             debian:buster
             debian:bullseye
             debian:sid
 
-            ubuntu:zesty
-
             centos:centos7
             almalinux:8
           "