Some more #ifdef cleanups

src/cmd/ksh93/edit/edit.c,
src/cmd/ksh93/edit/history.c,
src/cmd/ksh93/sh/deparse.c:
- Remove experimental code protected by '#ifdef future'.
  No one is going to do anything with this, it's just clutter.

src/lib/libast/sfio/sfcvt.c:
- In 2021, it might be time to actually start using some C99
  features were available. Change two checks for a _c99_in_the_wild
  macro to actual checks for C99, enabling the use of fpclassify().

Resolves: https://github.com/ksh93/ksh/issues/219

src/cmd/ksh93/sh/deparse.c

@@ -476,15 +476,8 @@ static void p_redirect(register const struct ionod *iop)
 		if(iop->iodelim)
 		{
 			/* here document */
-#ifdef xxx
-			iop->iolink = (char*)here_doc;
-#endif
 			here_doc  = iop;
 			io_op[2] = '<';
-#ifdef future
-			if(iof&IOSTRIP)
-				io_op[3] = '-';
-#endif
 		}
 		sfputr(outfile,cp,' ');
 		if(iop->ionxt)
@@ -586,11 +579,6 @@ static void p_switch(register const struct regnod *reg)
 static void here_body(register const struct ionod *iop)
 {
 	Sfio_t *infile;
-#ifdef xxx
-	if(iop->iolink)
-		here_body((struct inode*)iop->iolink);
-	iop->iolink = 0;
-#endif
 	if(iop->iofile&IOSTRG)
 		infile = sfnew((Sfio_t*)0,iop->ioname,iop->iosize,-1,SF_STRING|SF_READ);
 	else