Remove obsolete and partial crash workaround (re: 61437b2, 51b2e36)

The fix for #103 was incomplete and papered over the problem. The
real fix for this bug was applied in 51b2e36 on 20th February 2021.
That crash was the same one triggered differently.

#103 (comment)

src/cmd/ksh93/sh/io.c

@@ -2125,17 +2125,12 @@ static int	io_prompt(Sfio_t *iop,register int flag)
 	char *endprompt;
 	static short cmdno;
 	int sfflags;
-	int was_ttywait_on;
 	if(flag<3 && !sh_isstate(SH_INTERACTIVE))
 		flag = 0;
 	if(flag==2 && sfpkrd(sffileno(iop),buff,1,'\n',0,1) >= 0)
 		flag = 0;
 	if(flag==0)
 		return(sfsync(sfstderr));
-	/* Temporarily disable 'set -o notify' while expanding the prompt to avoid
-	   possible crashes (https://github.com/ksh93/ksh/issues/103). */
-	was_ttywait_on = sh_isstate(SH_TTYWAIT);
-	sh_offstate(SH_TTYWAIT);
 	sfflags = sfset(sfstderr,SF_SHARE|SF_PUBLIC|SF_READ,0);
 	if(!(sh.prompt=(char*)sfreserve(sfstderr,0,0)))
 		sh.prompt = "";
@@ -2197,8 +2192,6 @@ static int	io_prompt(Sfio_t *iop,register int flag)
 done:
 	if(*sh.prompt && (endprompt=(char*)sfreserve(sfstderr,0,0)))
 		*endprompt = 0;
-	if(was_ttywait_on)
-		sh_onstate(SH_TTYWAIT);  /* re-enable 'set -o notify' */
 	sfset(sfstderr,sfflags&SF_READ|SF_SHARE|SF_PUBLIC,1);
 	return(sfsync(sfstderr));
 }