Remove undefined method logicalIndex

The method isn't used and not even defined.

Change-Id: If442806e8d4b7e5ac8f83bc783163c02bbabf47f
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/accessible/itemviews_p.h

@@ -144,8 +144,6 @@ public:
 
 private:
     QModelIndex indexFromLogical(int row, int column = 0) const;
-
-    inline int logicalIndex(const QModelIndex &index) const;
 };
 #endif