Simplify Grafana metadata support

Change-Id: Ib09ad29f741ea99233c4a1375e32d06a14e345a3
diff --git a/etcd/meta/grafana.yml b/etcd/meta/grafana.yml
index f189fd7..a1af210 100644
--- a/etcd/meta/grafana.yml
+++ b/etcd/meta/grafana.yml
@@ -1,23 +1,12 @@
 {%- from "etcd/map.jinja" import server with context %}
 
 dashboard:
-{%- if server.monitoring is defined %}
-  {%- set backend = server.monitoring.get('backend') %}
-  {%- if backend is string %}
-    {%- set backend = [backend] %}
-  {%- endif %}
-{%- else %}
-{# legacy StackLight behavior #}
-{% set backend = ['influxdb'] %}
-{%- endif %}
-
-{%- if 'prometheus' in backend %}
   etcd-cluster-prometheus:
+    datasource: prometheus
     format: json
     template: etcd/files/grafana_dashboards/etcd_prometheus.json.json
-{%- endif %}
-{%- if 'influxdb' in backend %}
   etcd:
+    datasource: influxdb
     format: json
     template: etcd/files/grafana_dashboards/etcd_influxdb.json
   main: