Revert k8s.gcr.io vanity domain

This reverts commit eba5b6092a.

Fixes https://github.com/kubernetes/kubernetes/issues/57526

hack/testdata/multi-resource-json-modify.json

@@ -43,7 +43,7 @@
        "spec":{
          "containers":[{
            "name": "mock-container",
-           "image": "k8s.gcr.io/pause:2.0",
+           "image": "gcr.io/google-containers/pause:2.0",
            "ports":[{
              "containerPort":9949,
              "protocol":"TCP"