Re #6518. Removing unused header from framework/nexus package.
Re #6518. Removing nexus c-api from MuonNexusReader.
Re #6518. Moved integer status returns to exceptions.
Re #6518. Removing unnecessary includes.
Re #6518. Checkpointing work on the napi.h purge.
Re #6518. Moved to the nexus cpp api from c api.