Remove unused externs.

Author: bicknellr

externs/polymer-externs.js

@@ -138,15 +138,9 @@ Polymer.syncInitialRender;
 /** @type {boolean} */
 Polymer.legacyUndefined;
 
-/** @type {boolean} */
-Polymer.legacyNoBatch;
-
 /** @type {boolean} */
 Polymer.legacyWarnings;
 
-/** @type {boolean} */
-Polymer.legacyNotifyOrder;
-
 /** @type {boolean} */
 Polymer.orderedComputed;