Fixed #14495 -- DeletionMixin and FormMixin don't have an object to work with...

Fixed #14495 -- DeletionMixin and FormMixin don't have an object to work with so they cannot redirect to get_absolute_url and shouldn't claim they do.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14284 bcc190cf-cafb-0310-a4f2-bffc1f526a37