Moved Dspace Metadata RDF Mapping to digital-repositories.org.

The Vocabular to describe mappings between DSpace metadata fields and
RDF was moved to digital-repositories.org. I want to create a Digital
Repositories Ontology there and think that's a better place then the
domain of my personal web space.

Removed the files under dspace-rdf/src/main/resources as they were
redundant and not needed.