dropped slightly odd Conv.tap_thy

--- a/src/Pure/conv.ML	Fri Dec 17 18:24:44 2010 +0100
+++ b/src/Pure/conv.ML	Fri Dec 17 18:32:40 2010 +0100
@@ -48,7 +48,6 @@
   val concl_conv: int -> conv -> conv
   val fconv_rule: conv -> thm -> thm
   val gconv_rule: conv -> int -> thm -> thm
-  val tap_thy: (theory -> conv) -> conv
 end;
 
 structure Conv: CONV =
@@ -212,9 +211,6 @@
       end
   | NONE => raise THM ("gconv_rule", i, [th]));
 
-
-fun tap_thy conv ct = conv (Thm.theory_of_cterm ct) ct;
-
 end;
 
 structure Basic_Conv: BASIC_CONV = Conv;