keychain: use T.TempDir to create temporary test directory

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

keychain/bench_test.go

@@ -8,15 +8,11 @@ import (
 )
 
 func BenchmarkDerivePrivKey(t *testing.B) {
-	cleanUp, wallet, err := createTestBtcWallet(
-		CoinTypeBitcoin,
-	)
+	wallet, err := createTestBtcWallet(t, CoinTypeBitcoin)
 	require.NoError(t, err, "unable to create wallet")
 
 	keyRing := NewBtcWalletKeyRing(wallet, CoinTypeBitcoin)
 
-	defer cleanUp()
-
 	var (
 		privKey *btcec.PrivateKey
 	)