Bug 25360: (follow-up) Remove the https FIXME in Auth.pm

Bug 25360: (follow-up) Remove the https FIXME in Auth.pm

The FIXME is no longer valid since we fixed the X-Forwarded headers
for Plack. And since we do not even use using_https anymore in
the templates (see bug 21094).

Test plan:
Run Auth.t
Git grep for using_https

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 5f6fb719bf6f6e6e0f830f97561ddc6e29012071)