Update NotificationTechnicalFailureException

- Change the NotificationTechnicalFailureException so that it only inherits from Exception.
- The notify_celery task should create the logging message on failure.
- Fix unit tests
- Remove named parameter when raising exception.

app/exceptions.py

@@ -4,8 +4,7 @@ class DVLAException(Exception):
 
 
 class NotificationTechnicalFailureException(Exception):
-    def __init__(self, message):
-        self.message = message
+    pass
 
 
 class ArchiveValidationError(Exception):