Refs #29444 -- Allowed returning multiple fields from INSERT statements on PostgreSQL.

Thanks Florian Apolloner, Tim Graham, Simon Charette, Nick Pope, and
Mariusz Felisiak for reviews.

tests/backends/models.py

@@ -5,10 +5,6 @@ from django.contrib.contenttypes.models import ContentType
 from django.db import models
 
 
-class NonIntegerAutoField(models.Model):
-    creation_datetime = models.DateTimeField(primary_key=True)
-
-
 class Square(models.Model):
     root = models.IntegerField()
     square = models.PositiveIntegerField()