refactor(Angular.js): prevent Error variable name leak in tests

Remove var Error = window.Error

window.Error is a read-only property in Apps Script.

Igor says, "we should just delete that line instead. I think it was
misko's attempt to get better closure minification, but it turns out
that it's actually hurting us after gzip (I verified it)."

src/Angular.js

@@ -49,8 +49,7 @@ if ('i' !== 'I'.toLowerCase()) {
 function fromCharCode(code) {return String.fromCharCode(code);}
 
 
-var Error             = window.Error,
-    /** holds major version number for IE or NaN for real browsers */
+var /** holds major version number for IE or NaN for real browsers */
     msie              = int((/msie (\d+)/.exec(lowercase(navigator.userAgent)) || [])[1]),
     jqLite,           // delay binding since jQuery could be loaded after us.
     jQuery,           // delay binding