Proposal: Merge dna-chg (48004-6) and genomic-dna-chg (81290-9) into a single 1..1 HGVS variant expression, and remove fields that are implied by HGVS (transcript-ref_seq, genomic_ref_seq, ref-allele, alt-allele, allele-start-end)

*Rationale: *Too many ways to say the same thing. We can simply include an HGVS field, and remove all fields that are easily derivable from HGVS.