removed dead code;

--- a/src/Pure/pure_thy.ML	Sat Jul 28 22:00:59 2007 +0200
+++ b/src/Pure/pure_thy.ML	Sat Jul 28 22:01:00 2007 +0200
@@ -155,7 +155,6 @@
   fun copy (ref x) = ref x;
   val extend = mk_empty;
   fun merge _ = mk_empty;
-  fun print _ _ = ();
 end);
 
 val get_theorems_ref = TheoremsData.get;