Core/Achievements: port realm first achievement handling from master

veeeery partial cherry-pick of c75fcbe20b07fd7518be58bf02ba30d903133449

(cherry picked from commit 4596c17dae1dcb199b9301b7dcfd556bb1c0d7d5)

src/server/game/Maps/MapManager.cpp

@@ -34,7 +34,6 @@
 #include "Player.h"
 #include "WorldSession.h"
 #include "Opcodes.h"
-#include "AchievementMgr.h"
 
 MapManager::MapManager()
     : _nextInstanceId(0), _scheduledScripts(0)
@@ -395,5 +394,4 @@ void MapManager::FreeInstanceId(uint32 instanceId)
     // If freed instance id is lower than the next id available for new instances, use the freed one instead
     _nextInstanceId = std::min(instanceId, _nextInstanceId);
     _freeInstanceIds[instanceId] = true;
-    sAchievementMgr->OnInstanceDestroyed(instanceId);
 }