Remove alert(error) from email-browser.js

A few things here:
 - Firstly, you shouldn't be showing generic error messsages to end users
 - Secondly, alerting an error object always returns "Error: [Object object]" which isn't helpful even to developers, at least put that in console.log where it can be explained.
 - Thirdly, jQuery throws an AJAX error whenever the request is aborted. So if the user navigates away (clicks a link, presses the back button) before the request completes, they'll get an error message effectively interrupting their departure.