all: replace io/ioutil with io and os package

For golang/go#45557

Change-Id: I447530cc66896aef7a8d528ccb8d095b80e3cf47
GitHub-Last-Rev: 5f385ff46487ac318bd1147cdbbd26bb0ffd0426
GitHub-Pull-Request: golang/crypto#230
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/430797
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Meng Zhuo <mzh@golangcn.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

internal/wycheproof/wycheproof_test.go

@@ -12,7 +12,6 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
@@ -62,7 +61,7 @@ func TestMain(m *testing.M) {
 }
 
 func readTestVector(t *testing.T, f string, dest interface{}) {
-	b, err := ioutil.ReadFile(filepath.Join(wycheproofTestVectorsDir, f))
+	b, err := os.ReadFile(filepath.Join(wycheproofTestVectorsDir, f))
 	if err != nil {
 		t.Fatalf("failed to read json file: %v", err)
 	}