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- Use AST_VERSION instead of outdated _AST_VERSION.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/tests/basic.sh

@@ -693,7 +693,7 @@ got=$(set +x; { "$SHELL" -c '
 	echo baz				# 7
 '; } 2>&1)
 ((!(e = $?))) && [[ $got == "$exp" ]] || err_exit 'Redirection in DEBUG trap corrupts the trap' \
-	"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$got"))"
+	"(got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))"
 
 # The DEBUG trap crashed when re-trapping inside a subshell
 exp=$'trap -- \': main\' EXIT\ntrap -- \': main\' ERR\ntrap -- \': main\' KEYBD\ntrap -- \': main\' DEBUG'
@@ -707,7 +707,7 @@ got=$(set +x; { "$SHELL" -c '
 	done
 '; } 2>&1)
 ((!(e = $?))) && [[ $got == "$exp" ]] || err_exit 'Pseudosignal trap failed when re-trapping in subshell' \
-	"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$got"))"
+	"(got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))"
 
 # Field splitting broke upon evaluating an unquoted expansion in a DEBUG trap
 exp=$'a\nb\nc'
@@ -720,7 +720,7 @@ got=$(set +x; { "$SHELL" -c '
 	printf "%s\n" "$@"
 '; } 2>&1)
 ((!(e = $?))) && [[ $got == "$exp" ]] || err_exit 'Field splitting broke after executing DEBUG trap' \
-	"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$got"))"
+	"(got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))"
 
 # The DEBUG trap had side effects on the exit status
 trap ':' DEBUG