reverted wxPopupWindow implementation to the original version using WS_CHILD and desktop as parent; this fixes the activation problem but reopens the other ones

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15758 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/toplevel.h

@@ -99,9 +99,6 @@ protected:
     // choose the right parent to use with CreateWindow()
     virtual WXHWND MSWGetParent() const;
 
-    // we handle WM_NCACTIVATE specially here
-    virtual long MSWWindowProc(WXUINT msg, WXWPARAM wParam, WXLPARAM lParam);
-
     // is the window currently iconized?
     bool m_iconized;