Don't append aggregation tag to feature name when only a single method

[shntnu]

Revert this change #109

That's because

• changing the name complicates some of the analysis downstream
• the reason to include this was that we want to record what transformation was used. However this may not be a good way to store that info. Also, other steps e.g. normalization don't preserve this information. Further, if we were to follow this approach, we'd need to accumulate the tags as we move the data through the processing pipeline, and end up with names like Area_median_robustized_per_plate_... and so on, which is a terrible idea.
• aggregation tags do get appended when there is more than one method, e.g. mean+sd and that's ok because there's no other way to record it, while keeping the data tidy.