remove support for experimental 'lightdom' attribute.

Author: sorvell

src/declaration/polymer-element.js

@@ -44,6 +44,9 @@
       queue.register(this);
     },
 
+
+    // TODO(sorvell): refactor, this method is private-ish, but it's being
+    // called by the queue object.
     _register: function() {
       //console.log('registering', this.name);
       //console.group('registering', this.name);

src/instance/base.js

@@ -99,11 +99,7 @@
     parseDeclaration: function(elementElement) {
       var template = this.fetchTemplate(elementElement);
       if (template) {
-        if (this.element.hasAttribute('lightdom')) {
-          this.lightFromTemplate(template);
-        } else {
-          this.shadowFromTemplate(template);
-        }
+        this.shadowFromTemplate(template);
       }
     },
     // return a shadow-root template (if desired), override for custom behavior