Remove wxAuiMDIChildFrame::DoShow()

This method is confusing as it's not used for implementing Show(), which
is the usual naming convention when both Foo() and DoFoo() members
exist, and gives no clear indication about what does it really do.

Just call wxWindow::Show() directly instead.

Also create the wxAuiMDIChildFrame window hidden from the beginning,
instead of creating it in a visible state and then hiding it.

include/wx/aui/tabmdi.h

@@ -168,7 +168,6 @@ public:
     // we needed this function to prevent anybody from the outside
     // changing the panel... it messes the UI layout when we would allow it.
     void ApplyMDIChildFrameRect();
-    void DoShow(bool show);
 
 protected:
     wxAuiMDIParentFrame* m_pMDIParentFrame;