Revert k8s.gcr.io vanity domain

This reverts commit eba5b6092a.

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

test/e2e_node/runtime_conformance_test.go

@@ -275,13 +275,13 @@ while true; do sleep 1; done
 				},
 				{
 					description: "should not be able to pull non-existing image from gcr.io",
-					image:       "k8s.gcr.io/invalid-image:invalid-tag",
+					image:       "gcr.io/google_containers/invalid-image:invalid-tag",
 					phase:       v1.PodPending,
 					waiting:     true,
 				},
 				{
 					description: "should be able to pull image from gcr.io",
-					image:       "k8s.gcr.io/alpine-with-bash:1.0",
+					image:       "gcr.io/google_containers/alpine-with-bash:1.0",
 					phase:       v1.PodRunning,
 					waiting:     false,
 				},