nval.h: remove dtksh additions & old compat redefs (re: e2d1b593)

CDE <https://cdesktopenv.sf.net/> developer Chase writes, re dtksh:
| Everything is now completely working, and we are almost ready to
| add ksh93 as a submodule, but I have one last commit to get rid
| of some warnings we are facing. nval.h has some of these
| "compatiblity redefines" that are causing issues whenever we
| include it (warnings about redefining values) [...].

src/cmd/ksh93/include/nval.h:
- Replace ancient compatibility redefines by an unconditional
  '#include <hash.h>'; ksh works fine with the "new" hash library.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/include/nval.h

@@ -32,17 +32,7 @@
 #include	<ast.h>
 #include	<cdt.h>
 #include	<option.h>
-
-#ifdef BUILD_DTKSH
 #include	<hash.h>
-#endif
-
-/* for compatibility with old hash library */
-#define Hashtab_t	Dt_t
-#define HASH_BUCKET	1
-#define HASH_NOSCOPE	2
-#define HASH_SCOPE	4
-#define hashscope(x)	dtvnext(x)
 
 typedef struct Namval Namval_t;
 typedef struct Namfun Namfun_t;
@@ -115,9 +105,6 @@ struct Namdecl
 /* This defines the attributes for an attributed name-value pair node */
 struct Namval
 {
-#if BUILD_DTKSH
-	HASH_HEADER;                    /* space for hash library */
-#endif
 	Dtlink_t	nvlink;		/* space for cdt links */
 	char		*nvname;	/* pointer to name of the node */
 #if _ast_sizeof_pointer == 8