Revert "Make admin_notifications really optional"
Revert "Make admin_notifications really optional"

This reverts commit 2abd1e349d9caa53ec7cc0518402e4eb369a4a02.

Ixxy-Open-Source/django-linkcheck-old,yvess/django-linkcheck,DjangoAdminHackers/django-linkcheck,AASHE/django-linkcheck,Ixxy-Open-Source/django-linkcheck-old,DjangoAdminHackers/django-linkcheck,claudep/django-linkcheck,claudep/django-linkcheck