eliminated Attribute structure;

--- a/src/Pure/axclass.ML	Tue Jan 12 12:28:29 1999 +0100
+++ b/src/Pure/axclass.ML	Tue Jan 12 12:29:24 1999 +0100
@@ -225,7 +225,7 @@
       (map inclass super_classes @ map (int_axm o snd) axioms, inclass class);
   in
     thy
-    |> PureThy.add_axioms_i (map Attribute.none ((raw_class ^ "I", intro_axm) :: abs_axioms))
+    |> PureThy.add_axioms_i (map Thm.no_attributes ((raw_class ^ "I", intro_axm) :: abs_axioms))
   end;