dev: do not specify separate critical config file, only site config
Created by: sqs
Now that https://github.com/sourcegraph/sourcegraph/pull/7197 was merged (removing the management console and merging site config and critical config), it is not necessary to have separate files for site config and critical config.
After this PR is merged, anyone running enterprise/dev/start.sh
will be notified to update dev-private to a commit that incorporates https://github.com/sourcegraph/dev-private/pull/10 (which removes the dev-private critical-config.json file).