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/gengo/generator/import_tracker.go

@@ -1,64 +0,0 @@
-/*
-Copyright 2015 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 generator
-
-import (
-	"strings"
-
-	"k8s.io/klog"
-
-	"k8s.io/gengo/namer"
-	"k8s.io/gengo/types"
-)
-
-func NewImportTracker(typesToAdd ...*types.Type) namer.ImportTracker {
-	tracker := namer.NewDefaultImportTracker(types.Name{})
-	tracker.IsInvalidType = func(*types.Type) bool { return false }
-	tracker.LocalName = func(name types.Name) string { return golangTrackerLocalName(&tracker, name) }
-	tracker.PrintImport = func(path, name string) string { return name + " \"" + path + "\"" }
-
-	tracker.AddTypes(typesToAdd...)
-	return &tracker
-
-}
-
-func golangTrackerLocalName(tracker namer.ImportTracker, t types.Name) string {
-	path := t.Package
-
-	// Using backslashes in package names causes gengo to produce Go code which
-	// will not compile with the gc compiler. See the comment on GoSeperator.
-	if strings.ContainsRune(path, '\\') {
-		klog.Warningf("Warning: backslash used in import path '%v', this is unsupported.\n", path)
-	}
-
-	dirs := strings.Split(path, namer.GoSeperator)
-	for n := len(dirs) - 1; n >= 0; n-- {
-		// follow kube convention of not having anything between directory names
-		name := strings.Join(dirs[n:], "")
-		name = strings.Replace(name, "_", "", -1)
-		// These characters commonly appear in import paths for go
-		// packages, but aren't legal go names. So we'll sanitize.
-		name = strings.Replace(name, ".", "", -1)
-		name = strings.Replace(name, "-", "", -1)
-		if _, found := tracker.PathOf(name); found {
-			// This name collides with some other package
-			continue
-		}
-		return name
-	}
-	panic("can't find import for " + path)
-}