[1.6.x] Added missing deprecation note for model permission methods.
[1.6.x] Added missing deprecation note for model permission methods.

refs #20642.

Backport of e1dd24d2f from master.

felixjimenez/django,django-nonrel/django,redhat-openstack/django,django-nonrel/django,redhat-openstack/django,felixjimenez/django,felixjimenez/django,django-nonrel/django,redhat-openstack/django,django-nonrel/django,felixjimenez/django,redhat-openstack/django,dex4er/django,dex4er/django,dex4er/django