Revert security harness check to let developers push to dev.gitlab.org
Essentially reverts !3998 (merged). We actually need to be able to push to dev.gitlab.org for security MRs. Mirroring does not apply for security-*
branches, so they won't be automatically pushed to dev.gitlab.org (I misunderstood this during reviewing the initial MR).
Discussion in https://gitlab.slack.com/archives/CCFV016SV/p1584422270398100