mix of knowledge_source and primary_knowledge_source for edges files, even for ontologies

[realmarcin]

Here are the edge file headers for current transforms:
@bsantan

==> BacDive/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> BactoTraits/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> MediaDive/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> ontologies/chebi_edges.tsv <==
id subject predicate object relation knowledge_source

==> ontologies/ec_edges.tsv <==
subject predicate object relation primary_knowledge_source

==> ontologies/envo_edges.tsv <==
id subject predicate object relation knowledge_source meta

==> ontologies/go_edges.tsv <==
id subject predicate object relation knowledge_source

==> ontologies/ncbitaxon_edges.tsv <==
id subject predicate object relation knowledge_source

==> ontologies/upa_edges.tsv <==
subject predicate object relation primary_knowledge_source

==> RheaMappings/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> traits/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> uniprot_genome_features/edges.tsv <==
subject predicate object relation primary_knowledge_source

==> uniprot_genome_features/uniprot_bacdive_edges.tsv <==
subject predicate object relation primary_knowledge_source