Use honeypot_exempt instead of custom implementation

[Kristian Glass]

C-SSO-P uses django-honeypot

identityprovider.middleware.honeypot overrides HoneypodMiddleware.process_view to check for HONEYPOT_EXEMPT_URLS

This looks to predate django-honeypot gaining its own exemption functionality with the @honeypot_exempt decorator (https://github.com/jamesturk/django-honeypot/issues/10)

Casual inspection suggests that, though the two methods of expression differ, upstream functionality should be sufficient, so the implementation here could be dropped