Refs django#470 -- Adjusted Field.db_returning to be backend agnostic.

Determining if a field is db_returning based on the default connection
feature availability prevents the usage of RETURNING for db_default
fields in setups where non-default backends do support RETURNING.

Whether or not the field should be attempted to be returned is already
checked at the compiler level which is backend aware.

Author: charettes

django/db/models/fields/__init__.py

@@ -932,9 +932,7 @@ def db_tablespace(self):
     @property
     def db_returning(self):
         """Private API intended only to be used by Django itself."""
-        return (
-            self.has_db_default() and connection.features.can_return_columns_from_insert
-        )
+        return self.has_db_default()
 
     def set_attributes_from_name(self, name):
         self.name = self.name or name