QWizard: Fix frame when using Vista style/MSVC2012

Work around GetSystemMetrics() returning the wrong value using
MSVC2012 and later. The special handling of Windows 8 and later
is then no longer required.

[ChangeLog][QtWidgets][QWizard]  Fixed frame when using Vista style/MSVC2012.

Task-number: QTBUG-36192

Change-Id: I39c2ab70a266f12cd65fa740b10b86edffa60417
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from qtbase/852308114ff901b86cca99268f498fc1d56b622e)