Only include <unistd.h> under Unix in wxGTK code.

Also remove the inclusions of some Unix-specific headers that were not needed
at all.

Closes #14048.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

demos/forty/scorefil.cpp

@@ -20,11 +20,6 @@
 #include "wx/wx.h"
 #endif
 
-#ifdef __WXGTK__
-#include <unistd.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#endif
 #include "wx/textfile.h"
 #include "wx/config.h"
 #include "wx/fileconf.h"