We're trying to phase out the ELK systems. While we have agreed to not
immediately turn anything off we probably don't need to keep running the
system-config-legacy-logstash-filters job as ELK should remain fairly
fixed unless someone rewrites config management for it and modernizes
it. And if that happens they will want new modern testing too.
Depends-On: https://review.opendev.org/c/openstack/project-config/+/792710
Change-Id: I9ac6f12ec3245e3c1be0471d5ed17caec976334f