Remove wxApp::GetShell32Version().

This method was only used for checks for Windows 9x versions of shell32.

See ticket: #17120

include/wx/msw/app.h

@@ -102,10 +102,6 @@ public:
     // wasn't found at all
     static int GetComCtl32Version();
 
-    // the same for shell32.dll: returns 400, 471, 500, 600, ... (4.70 not
-    // currently detected)
-    static int GetShell32Version();
-
     // the SW_XXX value to be used for the frames opened by the application
     // (currently seems unused which is a bug -- TODO)
     static int m_nCmdShow;