Remove sent to dvla task

- task not really necessary as the status is already set to 'sending' before the task is called if it is not sending i.e. in reseach mode or using a test key

app/v2/notifications/post_notifications.py

@@ -20,7 +20,6 @@ from app.models import (
 )
 from app.celery.letters_pdf_tasks import create_letters_pdf
 from app.celery.research_mode_tasks import create_fake_letter_response_file
-from app.celery.tasks import update_letter_notifications_to_sent_to_dvla
 from app.notifications.process_notifications import (
     persist_notification,
     persist_scheduled_notification,
@@ -184,12 +183,6 @@ def process_letter_notification(*, letter_data, api_key, template, reply_to_text
                                               status=status,
                                               reply_to_text=reply_to_text)
 
-    if not should_send:
-        update_letter_notifications_to_sent_to_dvla.apply_async(
-            kwargs={'notification_references': [notification.reference]},
-            queue=QueueNames.RESEARCH_MODE
-        )
-
     if api_key.service.has_permission('letters_as_pdf'):
         if should_send:
             create_letters_pdf.apply_async(