special code setup for step function in IMP is redundant as definition was tuned (cf. c54d901d2946)

--- a/src/HOL/IMP/Collecting_Examples.thy	Wed Oct 10 10:48:17 2012 +0200
+++ b/src/HOL/IMP/Collecting_Examples.thy	Wed Oct 10 10:48:33 2012 +0200
@@ -7,12 +7,6 @@
 lemma insert_code [code]:  "insert x (set xs) = set (x#xs)"
 by simp
 
-text{* Make assignment rule executable: *}
-declare step.simps(2)[code del]
-lemma [code]: "step S (x ::= e {P}) = (x ::= e {(%s. s(x := aval e s)) ` S})"
-by auto
-declare step.simps(1,3-)[code]
-
 text{* The example: *}
 definition "c = WHILE Less (V ''x'') (N 3)
                 DO ''x'' ::= Plus (V ''x'') (N 2)"