block: drop paddings from structures

It makes no sense at all storing them in a structure, they're just a part of
encoding/decoding process.

pkg/core/block/block_base.go

@@ -35,9 +35,6 @@ type Base struct {
 	// Contract address of the next miner
 	NextConsensus util.Uint160
 
-	// Padding that is fixed to 1
-	_ uint8
-
 	// Script used to validate the block
 	Script transaction.Witness
 

pkg/core/block/header.go

@@ -10,8 +10,6 @@ import (
 type Header struct {
 	// Base of the block.
 	Base
-	// Padding that is fixed to 0.
-	_ uint8
 }
 
 // DecodeBinary implements Serializable interface.