Remove hard coded margins added by QGraphicsView::fitInView()

In QGraphicsView::fitInView(const QRectF &rect, Qt::AspectRatioMode aspectRatioMode)

    // Find the ideal x / y scaling ratio to fit \a rect in the view.
    int margin = 2;
    QRectF viewRect = viewport()->rect().adjusted(margin, margin, -margin, -margin);

The use of a hard coded margin value here should be removed as well as the corresponding adjusted.

This adds and unwanted, and unexpected margin to scene rect when using QGraphicsview::fitInView()