Remove -admin-* flags
The following discussion from !193 (merged) should be addressed:
If we try to start Pages with unknown flag it will fail, to err on the side of caution I decided to keep the flags definitions even if they are not needed/used, will remove them once changes (including in Omnibus) are released and propagated.
These can be removed in GitLab 13.0. We should update omnibus prior to that to stop setting them, though.