[release/1.4.8] core: update DAO soft-fork number, clean up the code

(cherry picked from commit ba784bdf36)

core/state/statedb.go

@@ -51,8 +51,6 @@ type StateDB struct {
 	txIndex      int
 	logs         map[common.Hash]vm.Logs
 	logSize      uint
-
-	reducedDao bool
 }
 
 // Create a new state from a given trie