bump internal libast version; various minor cleanups

These are minor things I accumulated over the last month or so.

Notable changes:

src/lib/libast/features/api,
src/lib/libast/misc/state.c,
src/lib/libast/comp/conf.tab,
src/cmd/ksh93/include/defs.h:
- Bump internal libast version to 20220101L. We've made a few
  additions to the API, at least pathicase (see 71934570, ca3ec200)
  and astconf_long (see c2ac69b2), so this should have been done
  already. This also updates '/opt/ast/bin/getconf _AST_VERSION'.
- Use AST_VERSION instead of outdated _AST_VERSION.
- In state.c, use AST_VERSION instead of hardcoding the version.

src/cmd/ksh93/sh/xec.c:
- Remove 'restorefd' variable, unused as of 42becab6.
- Remove 'cmdrecurse' function and SH_RUNPROG macro; this was once
  used by a few libcmd commands, but ast-open-archive reveals it's
  unused as of ast 1999-12-25.

src/cmd/ksh93/sh/*.c:
- Where available, use e_dot instead of "." for consistency; it is
  defined as an extern so we might as well use it.

src/cmd/ksh93/tests/*.sh:
- When reporting signal names in fails, include the SIG prefix.
- Fix a broken process hang test in subshell.sh.

src/lib/libast/man/sfdisc.3:
- Removed. The interfaces described here never made it out of AT&T;
  they do not exist in any libast version in ast-open-archive.
  Resolves: https://github.com/ksh93/ksh/issues/426

src/cmd/ksh93/include/shell.h

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1982-2012 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2021 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2022 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
 *                    by AT&T Intellectual Property                     *
@@ -469,8 +469,7 @@ extern int 		sh_waitsafe(void);
 extern int		sh_exec(const Shnode_t*,int);
 
 /*
- * As of 93u+m, direct access to sh is no longer obsolete, and
- * shgd ("global data") is no longer a separately allocated struct;
+ * As of 93u+m, direct access to sh is no longer obsolete;
  * sh_getinterp() is here for compatibility with the documented interface.
  */
 extern Shell_t		sh;
@@ -504,6 +503,5 @@ extern Shell_t		sh;
 #define SH_SIGSET	4
 #define SH_EXITSIG	0400	/* signal exit bit */
 #define SH_EXITMASK	(SH_EXITSIG-1)	/* normal exit status bits */
-#define SH_RUNPROG	-1022	/* needs to be negative and < 256 */
 
 #endif /* !shell_h_defined */