Amiga: collapse #ifndef CROSS_TO_AMIGA include forks

Every #include block had a paired NH: assign path for native builds.
Only the cross-compile path is built now.

sys/amiga/winamenu.c

@@ -3,15 +3,9 @@
  */
 /* NetHack may be freely redistributed.  See license for details. */
 
-#ifndef CROSS_TO_AMIGA
-#include "NH:sys/amiga/windefs.h"
-#include "NH:sys/amiga/winext.h"
-#include "NH:sys/amiga/winproto.h"
-#else
 #include "windefs.h"
 #include "winext.h"
 #include "winproto.h"
-#endif
 
 /* Start building the text for a menu */
 void