[FIX] stock,purchase: stop shortening picking type names

In purchase, a special key is set in the context to simplify the name
of the picking type: instead of the normal name, only the name of the
warehouse is used. This is problematic if more than one incoming picking
type exists for a given warehouse, as it prevents you from being able to
differentiate them. Asking users to modify the view to remove the
context key seem a bit too much to ask for something that should be
simple.

It is my understanding that this was implemented only for cosmetic
reasons, but I am willing to assume that having to select
"YourCompany: Delivery Orders" instead of simply
"YourCompany" for people who only have one picking type should not
be too disruptive or obscure.

opw-685751