[1.8.x] Removed unused import in example code in docs/topics/auth/default.txt

Backport of 10945ebeb8 from master

docs/topics/auth/default.txt

@@ -246,7 +246,7 @@ example, you can create the ``can_publish`` permission for a ``BlogPost`` model
 in ``myapp``::
 
     from myapp.models import BlogPost
-    from django.contrib.auth.models import Group, Permission
+    from django.contrib.auth.models import Permission
     from django.contrib.contenttypes.models import ContentType
 
     content_type = ContentType.objects.get_for_model(BlogPost)