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/conversion-gen/main.go

@@ -1,116 +0,0 @@
-/*
-Copyright 2016 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.
-*/
-
-// conversion-gen is a tool for auto-generating functions that convert
-// between internal and external types.  A general conversion code
-// generation task involves three sets of packages: (1) a set of
-// packages containing internal types, (2) a single package containing
-// the external types, and (3) a single destination package (i.e.,
-// where the generated conversion functions go, and where the
-// developer-authored conversion functions are).  The packages
-// containing the internal types play the role known as "peer
-// packages" in the general code-generation framework of Kubernetes.
-//
-// For each conversion task, `conversion-gen` will generate functions
-// that efficiently convert between same-name types in the two
-// (internal, external) packages.  The generated functions include
-// ones named
-//     autoConvert_<pkg1>_<type>_To_<pkg2>_<type>
-// for each such pair of types --- both with (pkg1,pkg2) =
-// (internal,external) and (pkg1,pkg2) = (external,internal).
-// Additionally: if the destination package does not contain one in a
-// non-generated file then a function named
-//     Convert_<pkg1>_<type>_To_<pkg2>_<type>
-// is also generated and it simply calls the `autoConvert...`
-// function.  The generated conversion functions use standard value
-// assignment wherever possible.  For compound types, the generated
-// conversion functions call the `Convert...` functions for the
-// subsidiary types.  Thus developers can override the behavior for
-// selected types.  For a top-level object type (i.e., the type of an
-// object that will be input to an apiserver), for such an override to
-// be used by the apiserver the developer-maintained conversion
-// functions must also be registered by invoking the
-// `AddConversionFuncs` method of the relevant `Scheme` object from
-// k8s.io/apimachinery/pkg/runtime.
-//
-// `conversion-gen` will scan its `--input-dirs`, looking at the
-// package defined in each of those directories for comment tags that
-// define a conversion code generation task.  A package requests
-// conversion code generation by including one or more comment in the
-// package's `doc.go` file (currently anywhere in that file is
-// acceptable, but the recommended location is above the `package`
-// statement), of the form:
-//   // +k8s:conversion-gen=<import-path-of-internal-package>
-// This introduces a conversion task, for which the destination
-// package is the one containing the file with the tag and the tag
-// identifies a package containing internal types.  If there is also a
-// tag of the form
-//   // +k8s:conversion-gen-external-types=<import-path-of-external-package>
-// then it identifies the package containing the external types;
-// otherwise they are in the destination package.
-//
-// For each conversion code generation task, the full set of internal
-// packages (AKA peer packages) consists of the ones specified in the
-// `k8s:conversion-gen` tags PLUS any specified in the
-// `--base-peer-dirs` and `--extra-peer-dirs` flags on the command
-// line.
-//
-// When generating for a package, individual types or fields of structs may opt
-// out of Conversion generation by specifying a comment on the of the form:
-//   // +k8s:conversion-gen=false
-package main
-
-import (
-	"flag"
-	"path/filepath"
-
-	"github.com/spf13/pflag"
-	"k8s.io/gengo/args"
-	"k8s.io/klog"
-
-	generatorargs "k8s.io/code-generator/cmd/conversion-gen/args"
-	"k8s.io/code-generator/cmd/conversion-gen/generators"
-	"k8s.io/code-generator/pkg/util"
-)
-
-func main() {
-	klog.InitFlags(nil)
-	genericArgs, customArgs := generatorargs.NewDefaults()
-
-	// Override defaults.
-	// TODO: move this out of conversion-gen
-	genericArgs.GoHeaderFilePath = filepath.Join(args.DefaultSourceTree(), util.BoilerplatePath())
-
-	genericArgs.AddFlags(pflag.CommandLine)
-	customArgs.AddFlags(pflag.CommandLine)
-	flag.Set("logtostderr", "true")
-	pflag.CommandLine.AddGoFlagSet(flag.CommandLine)
-	pflag.Parse()
-
-	if err := generatorargs.Validate(genericArgs); err != nil {
-		klog.Fatalf("Error: %v", err)
-	}
-
-	// Run it.
-	if err := genericArgs.Execute(
-		generators.NameSystems(),
-		generators.DefaultNameSystem(),
-		generators.Packages,
-	); err != nil {
-		klog.Fatalf("Error: %v", err)
-	}
-	klog.V(2).Info("Completed successfully.")
-}