Replace deprecated ioutil with io and os

https://pkg.go.dev/io/ioutil is deprecated since Go 1.16.

scripts/fork_go_templates/main.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -186,7 +185,7 @@ func doWithGoFiles(dir string,
 			return nil
 		}
 
-		data, err := ioutil.ReadFile(path)
+		data, err := os.ReadFile(path)
 		must(err)
 		f, err := os.Create(path)
 		must(err)