Remove demo data SQL and corresponding config option

Given the upcoming new Elasticsearch configuration index, it is no longer feasible to provide a demo configuration by simply inserting tags into the DB. This is due to the fact that at server startup, those tags will be loaded into the cache, but not the configuration index, and hence will not be searchable.

The proposed solution to provide a demo configuration is to use the client API directly from the hostmetrics (and testhandler) DAQ to automatically configure its own tags by itself.