[#577] Remove usages of deprecated io/ioutil

Signed-off-by: Angira Kekteeva <kira@nspcc.ru>

api/auth/signer/v4/v4.go

@@ -60,7 +60,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/url"
 	"sort"
@@ -367,7 +366,7 @@ func (v4 Signer) signWithBody(r *http.Request, body io.ReadSeeker, service, regi
 		if body != nil {
 			var ok bool
 			if reader, ok = body.(io.ReadCloser); !ok {
-				reader = ioutil.NopCloser(body)
+				reader = io.NopCloser(body)
 			}
 		}
 		r.Body = reader

api/layer/object_test.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
-	"io/ioutil"
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -22,7 +22,7 @@ func TestWrapReader(t *testing.T) {
 		streamHash.Write(buf)
 	})
 
-	dst, err := ioutil.ReadAll(wrappedReader)
+	dst, err := io.ReadAll(wrappedReader)
 	require.NoError(t, err)
 	require.Equal(t, src, dst)
 	require.Equal(t, h[:], streamHash.Sum(nil))