This was introduced in 2013 and removed in 2014, see log below:
git log -Saddress_form_simple
commit 510333288c
Author: Maikel Linke <mkllnk@web.de>
Date: Sun Mar 2 13:05:15 2014 +1100
first steps of new design
commit 2e1de9a6d3
Author: Rohan Mitchell <rohan@rohanmitchell.com>
Date: Fri Aug 23 13:12:36 2013 +1000
Fix admin create order - remove override on spree address form, update to spree patched to fix respond_override (spree issue #2210), fix nil state error
093edb66d3