addons: Remove Kubernetes Dashboard manifests and docs

* Stop maintaining Kubernetes Dashboard manifests. Dashboard takes
an unusual approch to security and is often a security weak point.
* Recommendation: Use `kubectl` and avoid using the dashboard. If
you must use the dashboard, explore hardening and consider using an
authenticating proxy rather than the dashboard's auth features

addons/dashboard/deployment.yaml

@@ -1,32 +0,0 @@
-apiVersion: extensions/v1beta1
-kind: Deployment
-metadata:
-  name: kubernetes-dashboard
-  namespace: kube-system
-spec:
-  replicas: 1
-  template:
-    metadata:
-      labels:
-        name: kubernetes-dashboard
-        phase: prod
-    spec:
-      containers:
-        - name: kubernetes-dashboard
-          image: gcr.io/google_containers/kubernetes-dashboard-amd64:v1.6.1
-          ports:
-            - name: http
-              containerPort: 9090
-          resources:
-            limits:
-              cpu: 100m
-              memory: 300Mi
-            requests:
-              cpu: 100m
-              memory: 100Mi
-          livenessProbe:
-            httpGet:
-              path: /
-              port: 9090
-            initialDelaySeconds: 30
-            timeoutSeconds: 30

addons/dashboard/service.yaml

@@ -1,15 +0,0 @@
-apiVersion: v1
-kind: Service
-metadata:
-  name: kubernetes-dashboard
-  namespace: kube-system
-spec:
-  type: ClusterIP
-  selector:
-    name: kubernetes-dashboard
-    phase: prod
-  ports:
-    - name: http
-      protocol: TCP
-      port: 80
-      targetPort: 9090