*: do not get private key from Account to check if it CanSign()

We have this API now to performs checks.

cli/smartcontract/smart_contract.go

@@ -892,7 +892,7 @@ func getUnlockedAccount(wall *wallet.Wallet, addr util.Uint160, pass *string) (*
 		return nil, fmt.Errorf("wallet contains no account for '%s'", address.Uint160ToString(addr))
 	}
 
-	if acc.PrivateKey() != nil {
+	if acc.CanSign() {
 		return acc, nil
 	}
 

pkg/consensus/consensus.go

@@ -377,7 +377,7 @@ func (s *service) getKeyPair(pubs []crypto.PublicKey) (int, crypto.PrivateKey, c
 			continue
 		}
 
-		if acc.PrivateKey() == nil {
+		if !acc.CanSign() {
 			err := acc.Decrypt(s.Config.Wallet.Password, s.wallet.Scrypt)
 			if err != nil {
 				s.log.Fatal("can't unlock account", zap.String("address", address.Uint160ToString(sh)))

pkg/services/notary/node.go

@@ -25,7 +25,7 @@ func (n *Notary) UpdateNotaryNodes(notaryNodes keys.PublicKeys) {
 	for _, node := range notaryNodes {
 		acc = n.wallet.GetAccount(node.GetScriptHash())
 		if acc != nil {
-			if acc.PrivateKey() != nil {
+			if acc.CanSign() {
 				break
 			}
 			err := acc.Decrypt(n.Config.MainCfg.UnlockWallet.Password, n.wallet.Scrypt)

pkg/services/oracle/nodes.go

@@ -30,7 +30,7 @@ func (o *Oracle) UpdateOracleNodes(oracleNodes keys.PublicKeys) {
 	for i := range oracleNodes {
 		acc = o.wallet.GetAccount(oracleNodes[i].GetScriptHash())
 		if acc != nil {
-			if acc.PrivateKey() != nil {
+			if acc.CanSign() {
 				break
 			}
 			err := acc.Decrypt(o.MainCfg.UnlockWallet.Password, o.wallet.Scrypt)