refactor tile serialize

include/td/game/Mobs.h

@@ -18,9 +18,6 @@ using Vec2fp = Vec2<FpFloat>;
 
 namespace game {
 
-
-struct WalkableTile;
-
 enum class EffectType : std::uint8_t {
 	Slowness = 0,
 	Stun,
@@ -127,6 +124,8 @@ class MobListener {
 	virtual void OnMobCastleDamage(Mob* damager, TeamCastle* enemyCastle, float damage) {}
 };
 
+using MobList = std::vector<MobPtr>;
+
 // typedef utils::ObjectNotifier<MobListener> MobNotifier;
 
 }  // namespace game