Move the kustomize binary to its own module.

cmd/kustomize/main.go

@@ -1,17 +0,0 @@
-// Copyright 2019 The Kubernetes Authors.
-// SPDX-License-Identifier: Apache-2.0
-
-package main
-
-import (
-	"os"
-
-	"sigs.k8s.io/kustomize/v3/pkg/commands"
-)
-
-func main() {
-	if err := commands.NewDefaultCommand().Execute(); err != nil {
-		os.Exit(1)
-	}
-	os.Exit(0)
-}