We should not be inferring the value for 'route_concept_id' in the
DRUG_EXPOSURE table, that should only be used if a source has verbatim data
to indicate the route. If its derived from the RxNorm concept, then
there's no reason to store it there, because it'd be a direct look-up in
the vocabulary. Also, while sometimes you may want to aggregate to
'Oral', other times, you may want to specificity of the type of
administration, so it would seem reasonable to offer a classification atop
RxNorm Dose Forms, but not as a replacement.