fix namespace selector issue

fixes grafana#795
removing the `namespaceSelector` from the network policy
effectively only allows pods from the same namespace to access
the image renderer. there is no need to manually specify the
namespace, and the label previously used to match on a namespace
isn't the default K8s namespace label (that would be
kubernetes.io/metadata.name )

Signed-off-by: Clément Nussbaumer <clement@astutus.org>

charts/grafana/templates/image-renderer-network-policy.yaml

@@ -64,10 +64,7 @@ spec:
         - port: {{ .Values.service.port }}
           protocol: TCP
       to:
-        - namespaceSelector:
-            matchLabels:
-              name: {{ template "grafana.namespace" . }}
-          podSelector:
+        - podSelector:
             matchLabels:
               {{- include "grafana.selectorLabels" . | nindent 14 }}
               {{- if .Values.podLabels }}