get rid of profcim Primitives

[VladimirAlexiev]

Similar to #28, there are several "Primitive" classes that are not useful in RDF (because there are builtin/standard analogs), and are in fact not used in any of the ontologies. So get rid of them.

Here they are, with a brief note

• profcim:IRI
  • This is just a IRI/URL. IRIs are a superset of URLs and there's no need to distinguish them
• profcim:URL
  • same
• profcim:StringIRI
  • The only difference from profcim:IRI is "serialized as rdf:resource in RDFXML" vs "serialized as literal without language"
  • So this corresponds to literal with datatype xsd:AnyURI. But that's only useful if the URI may include invalid chars: is that the intention here?
• profcim:StringFixedLanguage
  • this is xsd:string