kconfig/nconf: use the generic menu_get_ext_help()

nconf is the only front-end which does not use this helper, but prefer
to copy/paste the code. The test wrt. menu validity added in this
version of the code is bogus anyway as an invalid menu will get
dereferenced a few line below by calling menu_get_prompt().

For now, convert nconf to use menu_get_ext_help(), as do every other
front-end. We will deals with menu validity checks properly in a
separate commit.

Cc: Nir Tzachar <nir.tzachar@gmail.com>
Cc: Andrej Gelenberg <andrej.gelenberg@udo.edu>
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/nconf.c

@@ -1221,19 +1221,7 @@ static void conf_message_callback(const char *fmt, va_list ap)
 static void show_help(struct menu *menu)
 {
 	struct gstr help = str_new();
-
-	if (menu && menu->sym && menu_has_help(menu)) {
-		if (menu->sym->name) {
-			str_printf(&help, "%s%s:\n\n", CONFIG_, menu->sym->name);
-			str_append(&help, _(menu_get_help(menu)));
-			str_append(&help, "\n");
-			get_symbol_str(&help, menu->sym);
-		} else {
-			str_append(&help, _(menu_get_help(menu)));
-		}
-	} else {
-		str_append(&help, nohelp_text);
-	}
+	menu_get_ext_help(menu, &help);
 	show_scroll_win(main_window, _(menu_get_prompt(menu)), str_get(&help));
 	str_free(&help);
 }