Revert "[shell] Set DesktopView to black when no contents are loaded"

This reverts commit 0d02ac89

shell/desktopview.cpp

@@ -49,8 +49,6 @@ DesktopView::DesktopView(Plasma::Corona *corona, QScreen *targetScreen)
         setGeometry(targetScreen->geometry());
     }
 
-    setColor(Qt::black);
-
     setFlags(Qt::Window | Qt::FramelessWindowHint);
     setTitle(corona->kPackage().metadata().name());
     rootContext()->setContextProperty(QStringLiteral("desktop"), this);