block: drop Network from the Header

It's not network-tied any more, network is only needed to
sign/verify. Unfortunately we still have to keep network in consensus data
structures because of dbft library interface.

pkg/consensus/block_test.go

@@ -1,12 +1,11 @@
 package consensus
 
 import (
-	"crypto/rand"
 	"testing"
 
 	"github.com/nspcc-dev/dbft/block"
-	"github.com/nspcc-dev/dbft/crypto"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
 	"github.com/stretchr/testify/require"
@@ -14,10 +13,10 @@ import (
 
 func TestNeoBlock_Sign(t *testing.T) {
 	b := new(neoBlock)
-	priv, pub := crypto.Generate(rand.Reader)
+	priv, _ := keys.NewPrivateKey()
 
-	require.NoError(t, b.Sign(priv))
-	require.NoError(t, b.Verify(pub, b.Signature()))
+	require.NoError(t, b.Sign(&privateKey{PrivateKey: priv}))
+	require.NoError(t, b.Verify(&publicKey{PublicKey: priv.PublicKey()}, b.Signature()))
 }
 
 func TestNeoBlock_Setters(t *testing.T) {