Remove hack for bug in Chrome autocomplete

We added an extra, hidden, <input> to our /sign-in
and /register forms to stop Chrome's form
heuristics filling the fields in wrong.

See the commit that added it:

https://github.com/alphagov/notifications-admin/commit/33b15cdec6ce4eb4ad70a5e0701a2e49466cf825

This removes it after testing with the following
Chrome/OS combinations and all working without the
hack:

- Chrome 87, Windows 7
- Chrome 86, Windows 7
- Chrome 86, Windows 10
- Chrome 85, Windows 7
- Chrome 80, Windows 10
- Chrome 81, Windows 7
- Chrome 52, Windows 7
- Chrome 68, Windows 7
- Chrome 78, Windows 8.1
- Chrome 86, Windows 8.1

These combinations were based on the most-used
versions recorded in our analytics for the last 3
months.

app/templates/views/register.html

@@ -27,7 +27,6 @@ Create an account
           "classes": "govuk-!-width-three-quarters"
         }) }}
       </div>
-      <input class="govuk-visually-hidden" aria-hidden="true" tabindex="-1" id="defeat-chrome-autocomplete">
       {{ form.password(param_extensions={"hint": {"text": "At least 8 characters"}, "classes": "govuk-!-width-three-quarters", "autocomplete": "new-password"}) }}
       {{form.auth_type}}
       {{ page_footer("Continue") }}