VirtuosoInferenceModel: Cleanup

* Remove the type visibility code. We no longer rely on type visibility
for removing the ontology results.

* Temporarily disable the ontology graph group creation. It was created
in order to easily remove ontology results from Nepomuk queries.
However, virtuoso crashed a lot with the usage of graph group
exclusion.

Therefore graph groups aren't really used anywhere right now. Maybe
with future virtuoso versions. So, for now the code stays, but it is
not called.

Also added an appropriate warning in the function.