Remove on_demand from Api::CachedProductSerializer
Remove on_demand from Api::CachedProductSerializer

This fixes lots of specs like the whole
spec/controllers/shop_controller_spec.rb, almost all specs of
spec/lib/open_food_network/products_renderer_spec.rb and most of
spec/features/consumer/shopping/shopping_spec.rb.

mkllnk/openfoodnetwork,Matt-Yorkley/openfoodnetwork,openfoodfoundation/openfoodnetwork,Matt-Yorkley/openfoodnetwork,openfoodfoundation/openfoodnetwork,Matt-Yorkley/openfoodnetwork,mkllnk/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork,lin-d-hop/openfoodnetwork,Matt-Yorkley/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork