Remove standard prefixes

Could find no uses of these prefixes in the wild so there is a very slim chance
this is breaking.  It may however break within new microservices because mu is
not defined to be the commonly accepted value for the prefix.  Better be
explicit for now.

Author: madnificent

helpers/mu/sparql.js

@@ -44,11 +44,7 @@ function newSparqlClient(userOptions) {
     console.log(`Headers set on SPARQL client: ${JSON.stringify(options)}`);
   }
 
-  return new SparqlClient(process.env.MU_SPARQL_ENDPOINT, options).register({
-    mu: 'http://mu.semte.ch/vocabularies/',
-    muCore: 'http://mu.semte.ch/vocabularies/core/',
-    muExt: 'http://mu.semte.ch/vocabularies/ext/'
-  });
+  return new SparqlClient(process.env.MU_SPARQL_ENDPOINT, options);
 }
 
 /**