Remove sosa:isSampleOf from ANSIS entities

[abhritchie]

While conceptually valid, isSampleOf appears to duplicate what some of the has and related prefixed properties do on some entities.

E.g. SoilSite.relatedSoilBody creates the same relation as SoilSite.isSampleOf.

To keep things simple in the JSON schema I've removed isSampleOf so there is only one way to related entities. This also allows more explicit binding of particular types of entity.

[dr-shorthair]

isSampleOf is a very specific relationship, which says the context resource is designed to be representative of the target resource.
relatedX is more general.

[abhritchie]

Makes sense.

I'll start a discussion about the role of the JSON schema and how that will impact decisions about what to keep from the ontology. Ultimately, they are complimentary things that serve different purposes. The schema isn't replacing the ontology and may not need as much conceptual rigour.