Cleanup: parent + child slots both on Biosample - do we need them?

[bmeluch]

There are 5 slots on Biosample that I think are only meant to be used for grouping slots together, not to actually hold data:

• core_field
• environment_field
• investigation_field
• nucleic_acid_sequence_source_field
• sequencing_field

The first four have child slots on Biosample, sequencing_field children are on LibraryPreparation, NucleotideSequencing, and nowhere.
Montana mentioned that core_field is probably a relic of how MIxS is imported and may be changing anyway.

So, questions -

1. Can we take these 5 slots off of Biosample, since it doesn't make sense to populate them?
2. Are these slots helpful in other ways, do we need them at all?

[turbomam]

I am looking at this again now as part of my subsets review. I don't think there's any reason to keep them associated with Biosample

If they are being used to group other slots, maybe they should be marked is_grouping_slot . (Question to self: Or is that to indicate that they are the target of slot_group assertions?)

we do have the following empty subsets, which seem redundant

• environment
• investigation
• nucleic acid sequence source
• sequencing

I don't see any core subset