Don't show the MDI children implicitly by default in wxMSW any more.

We kept doing it for compatibility with pre-2.5.3 versions but this was a long
time ago and we don't need this any longer.

See #2508.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75944 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/mdi.h

@@ -225,7 +225,6 @@ protected:
     void Init();
 
 private:
-    bool m_needsInitialShow; // Show must be called in idle time after Creation
     bool m_needsResize; // flag which tells us to artificially resize the frame
 
     DECLARE_EVENT_TABLE()