Improve Observation.without_comments performance
Improve Observation.without_comments performance

Avoids  left outer join that's inherent in `missing`

MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer