Remove `stage-ci` Makefile target
Remove `stage-ci` Makefile target

This target is nowhere used and is just misleading that we run any job
with it. We usually use the k8s-ci-builder jobs for that purpose.

Signed-off-by: Sascha Grunert <70ab469ddb2ac3e35f32ed7c2fd1cca514b2e879@redhat.com>

kubernetes/release,kubernetes/release