bug 25013: Remove non needed import, it is already available in the window object

src/chrome/content/torbutton.js

@@ -13,8 +13,6 @@ let { unescapeTorString } = Cu.import("resource://torbutton/modules/utils.js", {
 let SecurityPrefs = Cu.import("resource://torbutton/modules/security-prefs.js", {});
 let { bindPrefAndInit, observe } = Cu.import("resource://torbutton/modules/utils.js", {});
 
-Cu.importGlobalProperties(["XMLHttpRequest"]);
-
 const k_tb_last_browser_version_pref = "extensions.torbutton.lastBrowserVersion";
 const k_tb_browser_update_needed_pref = "extensions.torbutton.updateNeeded";
 const k_tb_last_update_check_pref = "extensions.torbutton.lastUpdateCheck";