Fix the orphan endpoint
In the previous commit we prevented anyone from orphaning packages
but we prevented admins from doing it, which isn't what we meant to
do, admins should be allowed to orphan any packages since sometime
people become non-responsive.
This commit fixes this, we now only allow the current main admin or
admins to orphan packages.
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>