Update to use one less proxy per element

lib/src/js/polymer_bind_dart.html

Index: lib/src/js/polymer_bind_dart.html
diff --git a/lib/src/js/polymer_bind_dart.html b/lib/src/js/polymer_bind_dart.html
index c10ca9f9c4cf8be584d8df1deebe9e767ca38e6e..dcb0c3fa182eedd9ddda2c16e11cb7c37ceb4e77 100644
--- a/lib/src/js/polymer_bind_dart.html
+++ b/lib/src/js/polymer_bind_dart.html
@@ -5,13 +5,6 @@ BSD-style license that can be found in the LICENSE file.
 -->
 <script>
 if (Polymer.Bind) {
-  // Overwrite prepareInstance to a no-op for dart elements.
-  Polymer.Bind._originalPrepareInstance = Polymer.Bind.prepareInstance;
-  Polymer.Bind.prepareInstance = function (inst) {
-    if (inst.__isPolymerDart__) return;
-    this._originalPrepareInstance(inst);
-  };
-
   // We always need to create property accessors for dart elements, because we
   // always have `effects` (updating the dart class).
   // TODO(jakemac): Investigate making the updating of the dart class be an