Revert revision 27542 "Make Dart_IdentityEqual live up to its spec and not leak boxing implementati…

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 27544)
+++ runtime/vm/object.h	(working copy)
@@ -3739,10 +3739,6 @@
                     const AbstractTypeArguments& type_instantiator,
                     Error* bound_error) const;
 
-  // Check whether this instance is identical to the argument according to the
-  // specification of dare:core's identical().
-  bool IsIdenticalTo(const Instance& other) const;
-
   bool IsValidNativeIndex(int index) const {
     return ((index >= 0) && (index < clazz()->ptr()->num_native_fields_));
   }