Prevent login completion at page rendering

<input login `request.get("__ac")` > removed

When the login form is rendered, the username is not already completed.
We assume that the "__ac" cookie is deleted, so no need to generate the
login name server side. It also avoids to use the old "__ac" cookies.
Browsers are already able to autocomplete them just by clicking on the field.
erp5_commerce_widget_library __ac_persistent set to 0