Remove -Ofair option from celery worker

In version 4.0 of celery, -Ofair became the default
scheduling strategy:
https://docs.celeryproject.org/en/latest/history/whatsnew-4.0.html?highlight=fair#ofair-is-now-the-default-scheduling-strategy

This appears to still be the case:
5d68d781de/celery/concurrency/asynpool.py (L80)

Note, it took me a while to be certain of this as the documentation
for the celery CLI suggests a choice of `default` or `fair` which
isn't so useful as both of these are `fair`:
https://docs.celeryproject.org/en/latest/reference/cli.html#cmdoption-celery-worker-O

scripts/paas_app_wrapper.sh

@@ -29,7 +29,7 @@ case $NOTIFY_APP_NAME in
     -Q periodic-tasks 2> /dev/null
     ;;
   delivery-worker-reporting)
-    exec scripts/run_app_paas.sh celery -A run_celery.notify_celery worker --loglevel=INFO --concurrency=2 -Ofair \
+    exec scripts/run_app_paas.sh celery -A run_celery.notify_celery worker --loglevel=INFO --concurrency=2 \
     -Q reporting-tasks 2> /dev/null
     ;;
   delivery-worker-priority)