[1.11.x] Fixed #27742 -- Reverted "Fixed #24607 -- Serialized natural keys in multi-table inheritance models."

This reverts commit 74a575eb7296fb04e1fc2bd4e3f68dee3c66ee0a as it causes
unexpected migrations and doesn't seem to be the best solution.

Backport of 0595bca221825c0c6bd572a32f3bf9eff7069328 from master

2 files changed, 2 insertions, 13 deletions

diff --git a/django/core/serializers/base.py b/django/core/serializers/base.py
index 46fb25ea78..ae3866172b 100644
--- a/django/core/serializers/base.py
+++ b/django/core/serializers/base.py
@@ -88,7 +88,7 @@ class Serializer(object):
                         if self.selected_fields is None or field.attname in self.selected_fields:
                             self.handle_field(obj, field)
                     else:
-                        if self.field_is_selected(field) and self.output_pk_field(obj, field):
+                        if self.selected_fields is None or field.attname[:-3] in self.selected_fields:
                             self.handle_fk_field(obj, field)
             for field in concrete_model._meta.many_to_many:
                 if field.serialize:
@@ -101,12 +101,6 @@ class Serializer(object):
         self.end_serialization()
         return self.getvalue()
 
-    def field_is_selected(self, field):
-        return self.selected_fields is None or field.attname[:-3] in self.selected_fields
-
-    def output_pk_field(self, obj, pk_field):
-        return self.use_natural_primary_keys or pk_field != obj._meta.pk
-
     def start_serialization(self):
         """
         Called when serializing of the queryset starts.
diff --git a/django/db/models/options.py b/django/db/models/options.py
index 335289beea..1f1fb4bd75 100644
--- a/django/db/models/options.py
+++ b/django/db/models/options.py
@@ -13,7 +13,6 @@ from django.db import connections
 from django.db.models import Manager
 from django.db.models.fields import AutoField
 from django.db.models.fields.proxy import OrderWrt
-from django.db.models.fields.related import OneToOneField
 from django.db.models.query_utils import PathInfo
 from django.utils import six
 from django.utils.datastructures import ImmutableList, OrderedSet
@@ -298,11 +297,7 @@ class Options(object):
     def setup_pk(self, field):
         if not self.pk and field.primary_key:
             self.pk = field
-            # If the field is a OneToOneField and it's been marked as PK, then
-            # this is a multi-table inheritance PK. It needs to be serialized
-            # to relate the subclass instance to the superclass instance.
-            if not isinstance(field, OneToOneField):
-                field.serialize = False
+            field.serialize = False
 
     def setup_proxy(self, target):
         """