Deletion API with obsinn

[intarga]

The way obsinn communicates deletion right now is by sending a new message with a station_id (nationalnummer) and timestamp(s) that just doesn't include any params it wants needed. I believe this was designed with kvalobs in mind because it fits the kvalobs schema quite well, but it's madness for anyone else.

The ideal way forward is to make a new endpoint/message for deletion that's more specific, Søren has agreed to this, but whoever picks this issue up will need to coordinate with him on design and implementation.