Get rid of QtCreateControl() from wxQt code base

If possible, all windows should call wxWindow::Create() on creation now,
because among other things:
- It manages generic and non-generic windows uniformly and transparently
- It ensures an appropriate initial size for the window
- AddChild() and PostCreation() are automatically called
- Scrollbar policies are set in one place.

include/wx/qt/frame.h

@@ -13,7 +13,6 @@
 #include "wx/frame.h"
 
 class QMainWindow;
-class QAbstractScrollArea;
 
 class WXDLLIMPEXP_CORE wxFrame : public wxFrameBase
 {