Remove legacy code for older libast versions

Since ksh 93u+m comes bundled with libast 20111111, there's no need
to support older versions, so this is another cleanup opportunity.

src/cmd/ksh93/include/defs.h:
- Throw an #error if AST_VERSION is undefined or < 20111111.
  (Note that _AST_VERSION is the same as AST_VERSION, but the
  latter is newer and preferred; see src/lib/libast/features/api)

All other changed files:
- Remove legacy code for versions older than the currently used
  versions, which are:
  _AST_VERSION    20111111
  ERROR_VERSION   20100309
  GLOB_VERSION    20060717
  OPT_VERSION     20070319
  SFIO_VERSION    20090915
  VMALLOC_VERSION 20110808

src/cmd/ksh93/sh/string.c

@@ -703,15 +703,7 @@ char	*sh_fmtqf(const char *string, int single, int fold)
 
 const char *_sh_translate(const char *message)
 {
-#if ERROR_VERSION >= 20000317L
 	return(ERROR_translate(0,0,e_dict,message));
-#else
-#if ERROR_VERSION >= 20000101L
-	return(ERROR_translate(e_dict,message));
-#else
-	return(ERROR_translate(message,1));
-#endif
-#endif
 }
 
 /*
@@ -750,9 +742,7 @@ char *sh_checkid(char *str, char *last)
 	return(last);
 }
 
-#if	_AST_VERSION  <= 20000317L
 char *fmtident(const char *string)
 {
 	return((char*)string);
 }
-#endif