[Cleanup] Delete message.h (#3348)

# Notes
- This is unsued.

zone/CMakeLists.txt

@@ -228,7 +228,6 @@ SET(zone_headers
     lua_stat_bonuses.h
     map.h
     masterentity.h
-    message.h
     merc.h
     mob.h
     mob_movement_manager.h

zone/message.h

@@ -1,7 +0,0 @@
-struct Msg {
-	int		id;
-	char*	Sender;
-	char*	Subject;
-	char*	Body;
-	char*	Date;
-};