manifests: remove prometheus.io/scrape annotations

These annotations made sense in pre v1.3.0 Prometheus releases, however,
with >=v1.3.0 and the Prometheus Operator these annotations are more
confusing then helpful.

manifests/grafana/grafana-svc.yaml

@@ -4,8 +4,6 @@ metadata:
   name: grafana
   labels:
     app: grafana
-  annotations:
-    prometheus.io/scrape: 'true'
 spec:
   type: NodePort
   ports:
@@ -14,4 +12,4 @@ spec:
     protocol: TCP
     nodePort: 30902
   selector:
-    app: grafana
+    app: grafana