example: Don't show the dock widgets immediately

It's not needed, as they are going to be added to the layout.
Saves us from flicker and also the temporary floating position
being saved

examples/dockwidgets/MyMainWindow.cpp

@@ -196,7 +196,6 @@ KDDockWidgets::DockWidgetBase *MyMainWindow::newDockWidget()
     }
 
     dock->resize(600, 600);
-    dock->show();
     m_toggleMenu->addAction(dock->toggleAction());
 
     count++;