chore: remove orphaned deployment/polaris-rbac.yaml (PRI-917)

PR #146 moved RBAC management to the infra repo (Flux). The local
RBAC apply steps were removed from the E2E workflow, but this file
was inadvertently left behind. It is now orphaned since the
polaris-dashboard-proxy-reader Role and RoleBinding are managed
by Flux.

See PRI-916 for context.

deployment/polaris-rbac.yaml

@@ -1,28 +0,0 @@
-# RBAC to allow authenticated users to proxy to the Polaris dashboard service.
-# The polaris plugin reads audit data via the Kubernetes service proxy:
-#   /api/v1/namespaces/polaris/services/http:polaris-dashboard:80/proxy/results.json
-# Without this Role + RoleBinding, users get a 403 when Headlamp proxies the request.
-apiVersion: rbac.authorization.k8s.io/v1
-kind: Role
-metadata:
-  name: polaris-dashboard-proxy-reader
-  namespace: polaris
-rules:
-  - apiGroups: [""]
-    resources: ["services/proxy"]
-    resourceNames: ["polaris-dashboard", "http:polaris-dashboard:80"]
-    verbs: ["get"]
----
-apiVersion: rbac.authorization.k8s.io/v1
-kind: RoleBinding
-metadata:
-  name: polaris-dashboard-proxy-reader
-  namespace: polaris
-subjects:
-  - kind: Group
-    name: system:authenticated
-    apiGroup: rbac.authorization.k8s.io
-roleRef:
-  kind: Role
-  name: polaris-dashboard-proxy-reader
-  apiGroup: rbac.authorization.k8s.io