Leave pipeline status evaluation up to the clients

[timofurrer]

Today the foxops API has a feature to return an incarnation status, which basically checks the pipeline (if available) status and interprets if that incarnation is "successful" or not.

However, this assumption that this matters to all clients turns out to not really be the case, but just adds maintenance burden in foxops.

Let's remove it.

[defreng]

foxops already returns an additional merge_request_status field in the API responses, which is intended to replace the legacy status field.