Removed an update statement to notifications.

It's a small change, but we should remove any db operations that are not necessary.

app/notifications/process_letter_notifications.py

@@ -3,7 +3,7 @@ from app.models import LETTER_TYPE
 from app.notifications.process_notifications import persist_notification
 
 
-def create_letter_notification(letter_data, template, api_key, status, reply_to_text=None):
+def create_letter_notification(letter_data, template, api_key, status, reply_to_text=None, billable_units=None):
     notification = persist_notification(
         template_id=template.id,
         template_version=template.version,
@@ -19,6 +19,7 @@ def create_letter_notification(letter_data, template, api_key, status, reply_to_
         reference=create_random_identifier(),
         client_reference=letter_data.get('reference'),
         status=status,
-        reply_to_text=reply_to_text
+        reply_to_text=reply_to_text,
+        billable_units=billable_units
     )
     return notification

app/notifications/process_notifications.py

@@ -70,7 +70,8 @@ def persist_notification(
     simulated=False,
     created_by_id=None,
     status=NOTIFICATION_CREATED,
-    reply_to_text=None
+    reply_to_text=None,
+    billable_units=None
 ):
     notification_created_at = created_at or datetime.utcnow()
     if not notification_id:
@@ -94,6 +95,7 @@ def persist_notification(
         created_by_id=created_by_id,
         status=status,
         reply_to_text=reply_to_text,
+        billable_units=billable_units
     )
 
     if notification_type == SMS_TYPE: