Debugger: Revert parts of the 'arrayIndex' optimization

The parent's address is not always the base address of the array
data, but often a wrapper like QVector, so the correct computation
of the item's address is more involved, removing the benefits of
the optimization.

Change-Id: Iecb19799addc1502649fefbad0953b77947f4193
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/watchdata.h

@@ -53,7 +53,6 @@ public:
 
     QString expression() const;
     QString realName() const;
-    quint64 realAddress() const;
     QByteArray internalName() const;
     QString toToolTip() const;