Fixed redundant condition in the order "returned" state

[ridem]

In the way the "return" event in handled in Spree, there is a redundant condition that we could remove.

Line 65 in order/checkout.rb, the same condition appears already:

event :return do
  transition to: :returned,
             from: [:complete, :awaiting_return, :canceled],
             if: :all_inventory_units_returned?
end

It feels it's much better to put the eventual logic about the state machine in the order model rather than in the CustomerReturn model.

[TeatroIO]

I've prepared a stage to preview changes. Open stage or view logs.

[JDutil]

This appears to break the build if you could investigate please.

[bbonislawski]

I think that this is outdated already. If you think that it's not outdated, please mention me in comment and I'll reopen it