core: change block.ConsensusData to neo3 format

1. Dropped `Base.ConsensusData` block field

2. Added `Block.ConsensusData` field with `Nonce` and `PrimaryIndex`

3. Removed "Neo.Header.GetConsensusData" and
"AntShares.Header.GetConsensusData" interops

pkg/core/block/block_test.go

@@ -73,13 +73,16 @@ func newDumbBlock() *Block {
 			MerkleRoot:    hash.Sha256([]byte("b")),
 			Timestamp:     100500,
 			Index:         1,
-			ConsensusData: 1111,
 			NextConsensus: hash.Hash160([]byte("a")),
 			Script: transaction.Witness{
 				VerificationScript: []byte{0x51}, // PUSH1
 				InvocationScript:   []byte{0x61}, // NOP
 			},
 		},
+		ConsensusData: ConsensusData{
+			PrimaryIndex: 0,
+			Nonce:        1111,
+		},
 		Transactions: []*transaction.Transaction{
 			transaction.NewMinerTX(),
 			transaction.NewIssueTX(),