[2.1.x] Refs #29449 -- Removed release note for "Allowed using contrib.auth forms without installing contrib.auth."

The code was reverted in f3fa86a89b.
Backport of d3449faaa9 from master

docs/releases/2.1.txt

@@ -93,10 +93,6 @@ Minor features
 * :djadmin:`createsuperuser` now gives a prompt to allow bypassing the
   :setting:`AUTH_PASSWORD_VALIDATORS` checks.
 
-* :class:`~django.contrib.auth.forms.UserCreationForm` and
-  :class:`~django.contrib.auth.forms.UserChangeForm` no longer need to be
-  rewritten for a custom user model.
-
 :mod:`django.contrib.gis`
 ~~~~~~~~~~~~~~~~~~~~~~~~~