core/vm: move Log to core/types

This significantly reduces the dependency closure of ethclient, which no
longer depends on core/vm as of this change.

All uses of vm.Logs are replaced by []*types.Log. NewLog is gone too,
the constructor simply returned a literal.

cmd/disasm/main.go

@@ -18,10 +18,10 @@
 package main
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io/ioutil"
 	"os"
-	"encoding/hex"
 	"strings"
 
 	"github.com/ethereum/go-ethereum/core/vm"