remove cf stop to try and improve deploy robustness

Rationale:
Sometimes, when deploying, we've seen errors while stopping the old
apps: "(psycopg2.ProgrammingError) permission denied for relation notifications".

When you call cf stop, it may not be entirely synchronous. Under the
hood, cloudfoundry has to do a whole bunch of things when you stop an
app - it has its own internal db of what app states are, and also has
to remove it from any load balancers etc, and also it has to actually
stop the app. We're not sure if the `cf stop` command guarantees that
your process has already terminated by the time that the command
returns.

In our Makefile, we call `cf stop`, followed by `cf delete`. One
posisble theory is that the process is still running when `cf stop`
exits, and then `cf delete` unbinds that service from the database,
removing all of it's users' permissions.

This isn't confirmed, however, this commit removes the `cf stop`
command to see if it solves the issue. PaaS team confirmed that
it's redundant - `cf delete` will carry out the same tasks under
the hood.

Makefile

@@ -277,7 +277,6 @@ cf-deploy: ## Deploys the app to Cloud Foundry
 	cf rename ${CF_APP} ${CF_APP}-rollback
 	cf push ${CF_APP} -f ${CF_MANIFEST_FILE}
 	cf scale -i $$(cf curl /v2/apps/$$(cf app --guid ${CF_APP}-rollback) | jq -r ".entity.instances" 2>/dev/null || echo "1") ${CF_APP}
-	cf stop ${CF_APP}-rollback
 	cf delete -f ${CF_APP}-rollback
 
 .PHONY: cf-deploy-api-db-migration