Core/Grid:

- Simplified CellArea calculation (Original author: SilverIce)

- Removed unused code in Cell class (Original author: SilverIce)

- Improve some Visit functions.

src/server/game/Achievements/AchievementMgr.cpp

@@ -669,7 +669,6 @@ void AchievementMgr::SendAchievementEarned(AchievementEntry const* achievement)
         CellCoord p = Trinity::ComputeCellCoord(GetPlayer()->GetPositionX(), GetPlayer()->GetPositionY());
 
         Cell cell(p);
-        cell.data.Part.reserved = ALL_DISTRICT;
         cell.SetNoCreate();
 
         Trinity::AchievementChatBuilder say_builder(*GetPlayer(), CHAT_MSG_ACHIEVEMENT, LANG_ACHIEVEMENT_EARNED, achievement->ID);