Fix white text in tool tips and dock widget decorations

This was a regression in the custom styling. We no longer set
the panel property on the mainwindow but rely on qobject_cast
to style custom mainwindows.

Reviewed-by: thorbjorn

src/libs/utils/fancymainwindow.cpp

@@ -55,7 +55,6 @@ FancyMainWindowPrivate::FancyMainWindowPrivate() :
 FancyMainWindow::FancyMainWindow(QWidget *parent) :
     QMainWindow(parent), d(new FancyMainWindowPrivate)
 {
-    setProperty("panelwidget", true);
 }
 
 FancyMainWindow::~FancyMainWindow()