Quietly ignore extra personalisation

> If a user makes an API request with additional personalisation fields,
> we should simply discard any fields that the template doesn't have.
>
> This gives a couple of related advantages:
>
> - modifying template parameters no longer requires downtime for
>   clients - as they can pass in extra new parameters before a template
>   change, or continue passing in old unused parameters after removing
>   them from a template
>
> - services can pass in large user objects, for example, and then play
>   around with templates adding and removing fields at will
>
> we should make sure we still return an error if a user doesn't pass in
> a required parameter.

– https://www.pivotaltracker.com/story/show/140774195

app/template/rest.py

@@ -101,13 +101,6 @@ def preview_template_by_id_and_service_id(service_id, template_id):
             ]}, status_code=400
         )
 
-    if template_object.additional_data:
-        raise InvalidRequest(
-            {'template': [
-                'Personalisation not needed for template: {}'.format(", ".join(template_object.additional_data))
-            ]}, status_code=400
-        )
-
     data['subject'], data['content'] = template_object.subject, str(template_object)
 
     return jsonify(data)