remove the feature mapping to speed up STA queries

This removes the feature of interest mapping from the FROST views in order to signifcantly speed up the STA queries. This is definitively a rather harsh change but I think it might be acceptable for the following reasons:

• For static sensors/datastreams the same information is available in the LOCATION-Table and there it is easier to digest
• For dynamic sensors/datastreams the coordinates are always also present as related Datastreams and there easier and more efficiently accessible.

So we actually don't loose any information, just don't store it in the FeatureOfInterest table. I dunno, if we really need to bring it back at one point in the future, we still could do so. What do you guys think @bert.palm, @florian.gransee, @joost.hemmen1 ?