Another round of accumulated minor fixes and cleanups

Only notable changes listed below.

**/Mamfile:
- Do not bother redirecting standard error for 'cmp -s' to
  /dev/null. Normally, 'cmp -s' on Linux, macOS, *BSD, or Solaris
  do not not print any message. If it does, something unusual is
  going on and I would want to see the message.
- Since we now require a POSIX shell, we can use '!'.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/sh/init.c:
- Remove SH_TYPE_PROFILE symbol, unused after the removal of the
  SHOPT_PFSH code. (re: eabd6453)

src/cmd/ksh93/sh/io.c:
- piperead(), slowread(): Replace redundant sffileno() calls by
  the variables already containing their results. (re: 50d342e4)

src/cmd/ksh93/bltins/mkservice.c,
rc/lib/libcmd/vmstate.c:
- If these aren't compiled, define a stub function to silence the
  ranlib(1) warning that the .o file does not contain symbols.

src/cmd/ksh93/sh/init.c

@@ -1192,7 +1192,7 @@ int sh_type(register const char *path)
 				continue;
 			}
 		}
-		if (!(t & (SH_TYPE_PROFILE|SH_TYPE_RESTRICTED)))
+		if (!(t & SH_TYPE_RESTRICTED))
 		{
 			if (*s == 'r')
 			{
@@ -1222,7 +1222,7 @@ int sh_type(register const char *path)
 		if (!isalnum(*s))
 			return t;
 	}
-	return t & ~(SH_TYPE_KSH|SH_TYPE_PROFILE|SH_TYPE_RESTRICTED);
+	return t & ~(SH_TYPE_KSH|SH_TYPE_RESTRICTED);
 }
 
 
@@ -1948,7 +1948,6 @@ static Init_t *nv_init(void)
 /*
  * initialize name-value pairs
  */
-
 Dt_t *sh_inittree(const struct shtable2 *name_vals)
 {
 	register Namval_t *np;
@@ -2006,7 +2005,6 @@ Dt_t *sh_inittree(const struct shtable2 *name_vals)
  *
  * Returns pointer to A__z env var from which to import attributes, or 0.
  */
-
 static char *env_init(void)
 {
 	register char		*cp;