replace "dep" with "go mod"

A simple "go mod init && go mod tidy && go mod vendor" was enough and
mostly seems to have picked the same revisions of the dependencies as
before. Notable exceptions are klog and gogo/protobuf.

vendor/k8s.io/code-generator/cmd/client-gen/path/path.go

@@ -1,31 +0,0 @@
-/*
-Copyright 2017 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 path
-
-import "strings"
-
-// Vendorless removes the longest match of "*/vendor/" from the front of p.
-// It is useful if a package locates in vendor/, e.g.,
-// k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/apis/meta/v1, because gengo
-// indexes the package with its import path, e.g.,
-// k8s.io/apimachinery/pkg/apis/meta/v1,
-func Vendorless(p string) string {
-	if pos := strings.LastIndex(p, "/vendor/"); pos != -1 {
-		return p[pos+len("/vendor/"):]
-	}
-	return p
-}