[#1972] node: Fix object format unit tests

Includes:
1. Unused func removal;
2. Err check of the `Sign` method.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

CHANGELOG.md

@@ -14,6 +14,8 @@ Changelog for NeoFS Node
 - Correctly select the shard for applying tree service operations (#1996)
 - Physical child object removal by GC (#1699)
 - Increase error counter for write-cache flush errors (#1818)
+- Broadcasting helper objects (#1972)
+- `neofs-cli lock object`'s `lifetime` flag handling (#1972)
 
 ### Removed
 ### Updated

pkg/core/object/fmt_test.go

@@ -2,8 +2,6 @@ package object
 
 import (
 	"crypto/ecdsa"
-	"crypto/rand"
-	"crypto/sha256"
 	"strconv"
 	"testing"
 
@@ -19,15 +17,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func testSHA(t *testing.T) [sha256.Size]byte {
-	cs := [sha256.Size]byte{}
-
-	_, err := rand.Read(cs[:])
-	require.NoError(t, err)
-
-	return cs
-}
-
 func blankValidObject(key *ecdsa.PrivateKey) *object.Object {
 	var idOwner user.ID
 	user.IDFromKey(&idOwner, key.PublicKey)
@@ -89,7 +78,8 @@ func TestFormatValidator_Validate(t *testing.T) {
 		user.IDFromKey(&idOwner, ownerKey.PrivateKey.PublicKey)
 
 		tok := sessiontest.Object()
-		tok.Sign(ownerKey.PrivateKey)
+		err := tok.Sign(ownerKey.PrivateKey)
+		require.NoError(t, err)
 
 		obj := object.New()
 		obj.SetContainerID(cidtest.ID())