debugger: replace a workaround to update the [+] marker when items by a less intrusive one

src/plugins/debugger/watchhandler.h

@@ -233,7 +233,6 @@ private:
     void dump();
     void dumpHelper(WatchItem *item);
     void emitAllChanged();
-    Q_SLOT void resetExtraLayoutChanged();
 
 signals:
     void enableUpdates(bool);
@@ -245,9 +244,6 @@ private:
     WatchType m_type;
     WatchItem *m_root;
     QSet<QByteArray> m_fetchTriggered;
-    // Part of the workaround to update the [+] marker when items
-    // are added to a container.
-    bool m_inExtraLayoutChanged;
 };
 
 class WatchHandler : public QObject