Remove namespace for K8S monitoring

Kubernetes component metrics often have a namespace label themselves,
which is actually relevant. The target namespace label merely informs
where the scrape target is located, which is generally irrelevant for
these specific metrics.

manifests/prometheus/prometheus-k8s-cm.yaml

@@ -43,9 +43,6 @@ data:
       - action: keep
         source_labels: [__meta_kubernetes_service_name]
         regex: kubernetes|node-exporter|kube-state-metrics
-      - action: replace
-        source_labels: [__meta_kubernetes_namespace]
-        target_label: namespace
       - action: replace
         source_labels: [__meta_kubernetes_service_name]
         target_label: job