Remove in-tree credential plugins (again)

This change reverts three commits:

1. Revert "Revert "Remove gcp and azure auth plugins""
   This reverts commit 651b4f5b647a205d12fad4d0edc489d97109cccc.

2. Revert "update-gofmt"
   This reverts commit 79c09f0b310b8b66f8f14ad254f268788c42e076.

3. Revert "Update removal warnings to 1.26"
   This reverts commit 68758fc5c5099c83104a637e6d6ad3f4534f0d08.

Signed-off-by: Monis Khan <mok@microsoft.com>

Kubernetes-commit: 09cde58bbc13ff1229f61146221f56af4ff675dc

plugin/pkg/client/auth/gcp/gcp_stub.go

@@ -0,0 +1,36 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gcp
+
+import (
+	"errors"
+
+	"k8s.io/client-go/rest"
+	"k8s.io/klog/v2"
+)
+
+func init() {
+	if err := rest.RegisterAuthProviderPlugin("gcp", newGCPAuthProvider); err != nil {
+		klog.Fatalf("Failed to register gcp auth plugin: %v", err)
+	}
+}
+
+func newGCPAuthProvider(_ string, _ map[string]string, _ rest.AuthProviderConfigPersister) (rest.AuthProvider, error) {
+	return nil, errors.New(`The gcp auth plugin has been removed.
+Please use the "gke-gcloud-auth-plugin" kubectl/client-go credential plugin instead.
+See https://cloud.google.com/blog/products/containers-kubernetes/kubectl-auth-changes-in-gke for further details`)
+}