Revert "Give useful message for null derefs"

sdk/lib/core/null.dart

Index: sdk/lib/core/null.dart
diff --git a/sdk/lib/core/null.dart b/sdk/lib/core/null.dart
index f98218d173c16455d795758b4c9df0919c8a0ffb..dd914a3be90ae0ea66c2eabf9c7a0a5263f011af 100644
--- a/sdk/lib/core/null.dart
+++ b/sdk/lib/core/null.dart
@@ -16,8 +16,6 @@ class Null {
     throw new UnsupportedError('class Null cannot be instantiated');
   }
 
-  external dynamic noSuchMethod(Invocation invocation);
-
   /** Returns the string `"null"`. */
   String toString() => "null";
 }