Removal of preferred_scheme

⚠️ Change to our API for payment creation
We are removing the preferred_scheme_ids field inside payment_method.provider_selection (user_selected variant) in the POST /payments request.

While this should not lead to any request errors in existing integrations, we consider this a breaking change, as the preferences previously outlined in the field will not be taken into account anymore.

As far as we are aware, no currently live clients should observe a change in behaviour due to this change. Therefore, the removal will take place in two weeks (01/11/2022).

We will announce a more sophisticated replacement enabling scheme selection in the near future.

We've updated our documentation and our API to reflect this change.