removed the wait_for_ajax()

This is both a curious and cautious pull request. I believe that we can safely remove <code>wait_for_ajax()</code) with only positive effects.

I investigated <code>WebDriverWait(self.selenium, self.timeout).until(lambda s: s.execute_script('return (typeof jQuery !== "undefined" && jQuery.active == 0)'))</code> which was causing consistent errors due to timeouts.

I tested the removed <code>wait_for_ajax()</code> against both the <code>PHP</code> and <code>Django</code> apps.
The tests consistently all pass:
* dev
* stage
* prod