Do not pass self.store to field.populate

self.store is not defined in kiwi's layer, so it makes no sense to access it
here. Let who uses self.store access it, since field has access to it's form
and the form has access to it's view.

Change-Id: I6fbfd6028063f6cfa71b4097c4c8407b84de8204
Merge "Do not pass self.store to field.populate"