Do not set a custom format on QQuickWindows

All QQuickWindows share a default format. By setting a custom format
it overwrites the default and this results in a format without a
stencil buffer being requested resulting in possible rendering errors.

REVIEW: 118122

src/plasmaquick/dialog.cpp

@@ -413,9 +413,6 @@ Dialog::Dialog(QQuickItem *parent)
     : QQuickWindow(parent ? parent->window() : 0),
       d(new DialogPrivate(this))
 {
-    QSurfaceFormat format;
-    format.setAlphaBufferSize(8);
-    setFormat(format);
     setClearBeforeRendering(true);
     setColor(QColor(Qt::transparent));
     setFlags(Qt::FramelessWindowHint);

src/plasmaquick/view.cpp

@@ -159,10 +159,6 @@ View::View(Plasma::Corona *corona, QWindow *parent)
     : QQuickView(parent),
       d(new ViewPrivate(corona, this))
 {
-    QSurfaceFormat format;
-    format.setAlphaBufferSize(8);
-
-    setFormat(format);
     setColor(Qt::transparent);
 
     QObject::connect(screen(), &QScreen::geometryChanged,