Revert "onefile: isaac64.c <math.h> vs yn()"

This reverts commit 94945a719a.
It was too intrusive and can be handled by the 'onefile' script
by compiling isaac64.c before any source file that includes hack.h.

src/isaac64.c

@@ -7,25 +7,11 @@
  * Changes for NetHack:
  *      include config.h;
  *      skip rest of file if USE_ISAAC64 isn't defined there;
- *      yn() hackery;
  *      re-do 'inline' handling.
  */
 #include "config.h"
 
 #ifdef USE_ISAAC64
-/*
- * OSX <math.h> declares yn() in a section labelled
- * "POSIX/UNIX extensions to the C standard".
- *
- * Even when yn() is not a macro, expansion of nethack's yn() macro
- * would break it.  Matters for 'onefile' lint checking where contents
- * of hack.h will be visible even though we only include config.h.
- */
-#ifdef yn
-#undef yn
-#define _isaac64_hide_yn
-#endif
-
 #include <math.h>
 #include <string.h>
 #include "isaac64.h"
@@ -185,17 +171,6 @@ uint64_t isaac64_next_uint(isaac64_ctx *_ctx,uint64_t _n){
   while(((d+_n-1)&ISAAC64_MASK)<d);
   return v;
 }
-
-#ifdef _isaac64_hide_yn
-/* 'onefile' support; restore nethack's yn() macro;
-   this could be made more robust but doesn't need that */
-#ifdef yn
-#undef yn /* in case <math.h> defines yn() as a macro */
-#endif
-#define yn(query) yn_function(query, ynchars, 'n', TRUE)
-#undef _isaac64_hide_yn
-#endif
-
 #endif /* USE_ISAAC64 */
 
 /*isaac64.c*/