core: clean up routes left behind after last location was deleted

[Janos Gyerik]

Location deleting has a flow. Each location has a location id, and a route id, and multiple locations that belong to the same route have the same route id. The issue is when deleting a location, the route id should only be deleted if there are no more locations associated with it. Right now we use a lazy method, and not delete routes at all. One way of implementing this is add a delete query to delete all routes where route id is not in distinct route ids of location table.