Fix some deprecation warnings

tst_qvideoframe.cpp:736:68: warning: 'int QImage::byteCount() const' is deprecated: Use sizeInBytes [-Wdeprecated-declarations]
videowidget.cpp:103:49: warning: ‘const QBrush& QPalette::background() const’ is deprecated: Use QPalette::window() instead [-Wdeprecated-declarations]
videowidget.cpp:111:62: warning: ‘const QBrush& QPalette::background() const’ is deprecated: Use QPalette::window() instead [-Wdeprecated-declarations]

Change-Id: If6ba7de74c695cb5405ef7d3f9c5be8f94e3e522
Reviewed-by: VaL Doroshchuk <valentyn.doroshchuk@qt.io>

examples/multimediawidgets/customvideosurface/customvideowidget/videowidget.cpp

@@ -100,7 +100,7 @@ void VideoWidget::paintEvent(QPaintEvent *event)
             QRegion region = event->region();
             region = region.subtracted(videoRect);
 
-            QBrush brush = palette().background();
+            QBrush brush = palette().window();
 
             for (const QRect &rect : region)
                 painter.fillRect(rect, brush);
@@ -108,7 +108,7 @@ void VideoWidget::paintEvent(QPaintEvent *event)
 
         surface->paint(&painter);
     } else {
-        painter.fillRect(event->rect(), palette().background());
+        painter.fillRect(event->rect(), palette().window());
     }
 }
 //! [3]

tests/auto/unit/qvideoframe/tst_qvideoframe.cpp

@@ -733,7 +733,7 @@ void tst_QVideoFrame::mapImage()
     QVERIFY(frame.map(mode));
 
     QVERIFY(frame.bits());
-    QCOMPARE(frame.mappedBytes(), image.byteCount());
+    QCOMPARE(qsizetype(frame.mappedBytes()), image.sizeInBytes());
     QCOMPARE(frame.bytesPerLine(), image.bytesPerLine());
     QCOMPARE(frame.mapMode(), mode);