disableAutoGitUpdates disables all updates instead of just scheduled updates

Created by: slimsag

https://github.com/sourcegraph/deploy-sourcegraph-dot-com/blob/release/base/repo-updater/repo-updater.Deployment.yaml#L38-L39 sets it to 0 but the proper value would be -1.

Also we should not be setting it via environment var as that is no longer respected, we need to set in site config. The fix here should be:

1. Update the site config to ensure repo updater is off
2. Remove the env var from the deployment, verify it is also not in deploy-sourcegraph. (https://github.com/sourcegraph/deploy-sourcegraph-dot-com/pull/214)