replace clock skew alert with one provided by node_exporter mixin

jsonnet/kube-prometheus/alerts/node.libsonnet

@@ -1,24 +1,6 @@
 {
   prometheusAlerts+:: {
     groups+: [
-      {
-        name: 'node-time',
-        rules: [
-          {
-            alert: 'ClockSkewDetected',
-            annotations: {
-              message: 'Clock skew detected on node-exporter {{ $labels.namespace }}/{{ $labels.pod }}. Ensure NTP is configured correctly on this host.',
-            },
-            expr: |||
-              abs(node_timex_offset_seconds{%(nodeExporterSelector)s}) > 0.05
-            ||| % $._config,
-            'for': '2m',
-            labels: {
-              severity: 'warning',
-            },
-          },
-        ],
-      },
       {
         name: 'node-network',
         rules: [