colortable[] formatting

remove unused hexval field (show it in a comment)

The rgb values should be the same as they were
previously, just expressed with hex values on the
table initialization.

include/color.h

@@ -65,7 +65,6 @@ struct nethack_color {
     int tableindex;
     int rgbindex;
     const char *name;
-    const char *hexval;
     long r, g, b;
 };