remove customer field from OrderListSerializer
remove customer field from OrderListSerializer

This field polluted the global template_context namespace with `customer` causing template `shop/navbar/login-logout.html` to fail.
See also #622 for details how to prevent this in future.

nimbis/django-shop,khchine5/django-shop,awesto/django-shop,nimbis/django-shop,awesto/django-shop,khchine5/django-shop,divio/django-shop,nimbis/django-shop,divio/django-shop,khchine5/django-shop,khchine5/django-shop,divio/django-shop,nimbis/django-shop,awesto/django-shop