Remove unnecessary build warning

spacingHint()/marginHint() just returned the defaults from QApplication
even in kdelibs (4), so this code was useless.

The direct port would look something like this:
    page2Layout->setMargin(QApplication::style()->pixelMetric(QStyle::PM_DefaultChildMargin););
    page2Layout->setSpacing(QApplication::style()->pixelMetric(QStyle::PM_DefaultLayoutSpacing););