plug-ins: remove unnecessary Windows specific code in tinyscheme

Removal of the snprintf define was also part of the UCRT Windows patch
in MINGW. Although it builds fine without this change, there is no need
anymore to redefine snprintf. In addition, I seem to remember that
_snprintf had a shortcoming.

So let's remove the Windows specific code, since it works fine without it.

(cherry picked from commit e268d38fb1)

plug-ins/script-fu/tinyscheme/scheme.c

@@ -28,12 +28,6 @@
 #if HAVE_UNISTD_H
 # include <unistd.h>
 #endif
-#ifdef WIN32
-# include <io.h>
-#endif
-#ifdef WIN32
-#define snprintf _snprintf
-#endif
 #if USE_DL
 # include "dynload.h"
 #endif