Core/Dungeon Finder: revert r14440b0b82 and fix it properly.

That msg was just for debugging purposed and its not needed anymore

--HG--
branch : trunk

src/server/game/DungeonFinding/LFGMgr.cpp

@@ -723,10 +723,7 @@ void LFGMgr::Leave(Player* plr, Group* grp /* = NULL*/)
                 RemoveProposal(it, LFG_UPDATETYPE_PROPOSAL_DECLINED);
             break;
         }
-        case LFG_STATE_NONE:
-            break;
         default:
-            sLog.outError("LFGMgr::Leave: [" UI64FMTD "], state %u - This shouldn't happen", guid, uint8(state));
             break;
     }
 }