In cleanup commit 9cd05a8c39c6ed03688859de92372d93af5cc6e2 the labels on the ServiceMonitors were changed from k8s-apps to k8s-app. This commit makes the Prometheus selector match that change.
For `--dry-run` to work with kubectl a Kubernetes cluster's apiserver is
actually used, which is unnecessary for generating these manifests. This
approach also allows further customization, such as adding labels to the
generated manifests.