Remove configmap/config-file resource from Sourcegraph.com k8s

Created by: sqs

Sourcegraph.com's k8s deployment and dogfood's k8s deployment both still have a configmap/config-file resource that has settings set in it. We've seen that it makes it harder for other teammates to make changes if they are unsure of whether our own deployment is using legacy/deprecated functionality, so this resource should be removed or made 100% empty (so that anyone viewing it knows it is not relied upon, and all config is stored in the DB).

This blocked me when I was working on #929. I want to remove httpStrictTransportSecurity from it, but I don't know whether it is still in use. I could spend the time to confirm yes or no, but as long as it remains, anyone else in a similar situation would need to spend that same time, so it is better to just remove or empty it.

Related to #1538 (closed) but not the same (that issue is about removing it from deploy-sourcegraph, this one is about removing or emptying it in prod)