Revert "Merge branch 'docker_privileged_builds' into 'cern_gitlab_ci'"

This reverts merge request !1 (merged)

Rolling back as, for some reason, the privileged runners are not able to push the resulting docker images to the gitlab registry.

See: https://gitlab.cern.ch/paas-tools/origin/-/jobs/2114729. Please note the job is successful as the error occurs in the after_script section. I have tried to debug it myself but I don't know how the new privileged runners are configured.