Fixed #25685 -- Fixed a duplicate query regression on deletion of proxied models.

Thanks to Trac alias ppetrid for the report and Tim for the review.

Conflicts:
	django/db/models/deletion.py
	tests/delete/tests.py

Forward port of 7c3ef19978 from stable/1.8.x

tests/delete/models.py

@@ -99,6 +99,12 @@ class Avatar(models.Model):
     desc = models.TextField(null=True)
 
 
+# This model is used to test a duplicate query regression (#25685)
+class AvatarProxy(Avatar):
+    class Meta:
+        proxy = True
+
+
 class User(models.Model):
     avatar = models.ForeignKey(Avatar, models.CASCADE, null=True)