Core/Dungeon Finder: Fix group (5) unable to do new dungeon after finished last dungeon

- Some optimizations here and there
- Drop unused columns related to dungeon rewards
- Simplify Group reward. All people inside the dungeon should get the reward, no matter how far it's from the boss

src/server/game/Handlers/BattleGroundHandler.cpp

@@ -499,7 +499,7 @@ void WorldSession::HandleBattleFieldPortOpcode(WorldPacket &recvData)
     }
 }
 
-void WorldSession::HandleLeaveBattlefieldOpcode(WorldPacket& recvData)
+void WorldSession::HandleBattlefieldLeaveOpcode(WorldPacket& recvData)
 {
     sLog->outDebug(LOG_FILTER_NETWORKIO, "WORLD: Recvd CMSG_LEAVE_BATTLEFIELD Message");