Receiving items against a purchase order now makes use of the API forms

- Delete old unused code
- Improve serializer validation

InvenTree/part/serializers.py

@@ -193,6 +193,7 @@ class PartBriefSerializer(InvenTreeModelSerializer):
         fields = [
             'pk',
             'IPN',
+            'default_location',
             'name',
             'revision',
             'full_name',