Update polymer externs for new settings.

Author: kevinpschaaf

externs/polymer-externs.js

@@ -153,6 +153,9 @@ Polymer.orderedComputed;
 /** @type {boolean} */
 Polymer.fastDomIf;
 
+/** @type {boolean} */
+Polymer.removeNestedTemplates;
+
 /** @type {boolean} */
 Polymer.suppressTemplateNotifications;