remove unused prefix

config/ontologies.ttl

@@ -3,7 +3,6 @@
 @prefix fuseki:         <http://jena.apache.org/fuseki#> .
 @prefix ja:             <http://jena.hpl.hp.com/2005/11/Assembler#> .
 @prefix rdfs:           <http://www.w3.org/2000/01/rdf-schema#> .
-@prefix skos:           <http://www.w3.org/2004/02/skos/core#> .
 @prefix skos-last-call: <http://www.w3.org/2008/05/skos#> .
 @prefix spdx:           <http://spdx.org/rdf/terms#> .
 @prefix tdb2:           <http://jena.apache.org/2016/tdb#> .