Refactor to avoid creating individual instrument netcdfs

[callumrollo]

As per comments by @jklymak in PR #14:

Maybe we should go back though and simplify the logic, because the seperate sensor streams were a hack anyway, and not integral to the processing.

I wonder if we can get rid of this hack, and just process without the prefix at all? That greatly simplifies all this code and we don't need to assume anything about the carrier instrument for each sensor.