Use PassThrough renderer

Implements and depends on:
- [ ] https://github.com/alphagov/notifications-utils/pull/49

app/notifications/rest.py

@@ -9,6 +9,7 @@ from flask import (
 )
 from notifications_utils.recipients import allowed_to_send_to, first_column_heading
 from notifications_utils.template import Template
+from notifications_utils.renderers import PassThrough
 from app.clients.email.aws_ses import get_aws_responses
 from app import api_user, encryption, create_uuid, DATETIME_FORMAT, DATE_FORMAT, statsd_client
 from app.models import KEY_TYPE_TEAM
@@ -243,7 +244,7 @@ def send_notification(notification_type):
     template_object = Template(
         template.__dict__,
         notification.get('personalisation', {}),
-        renderer=lambda content: content
+        renderer=PassThrough()
     )
     if template_object.missing_data:
         message = 'Missing personalisation: {}'.format(", ".join(template_object.missing_data))