Make InRadius restriciton use GeoFilt class

This is mainly to allow 'q.without(:geo).in_radius(32, -68, 10, bbox: true)` functionality. That is, the use of `bbox` on `without` queries.

Also, since the `Sunspot::Query::Geofilt` already has the responsibility of generating the `geofilt` function for other types of queries, it makes sense to have `InRadius` use the same code and logic.