Remove name="submit" from checkout page submit buttons

If you hijack the form submission on the checkout page to run some javascript before the form gets submitted, it's then difficult(*) to make the JS submit the form. This is because the submit buttons have a name of "submit" - overriding the submit() method normally used to trigger form submission from JQuery:

See:
http://stackoverflow.com/questions/12853765/jquery-howto-submit-form-that-has-submit-button-with-the-name-submit

The pull request attached removes the names from the checkout fields. 

(*) I'm hoping it's not actually impossible or the plugin I'm working on is a dead-end, but at the very least it's annoyingly difficult.