(lnd_maxno): Variable's value is well-known constant N_MAXLAND + 1.

Useless, remove.  Users changed to check lchr's sentinel, because
that's clearer than comparing the index to N_MAXLAND or sizeof(lchr) /
sizeof(*lchr).

(lchr): Change sentinel's l_name to NULL.

src/lib/global/land.c

@@ -207,11 +207,9 @@ struct lchrstr lchr[] = {
 */
 
     {{0},
-     "",
+     NULL,
      0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0,
      }
 };
-
-int lnd_maxno = (sizeof(lchr) / sizeof(struct lchrstr)) - 1;