Drop Req Monitoring Feature as Feature Of Interest

Under V1.X, there was a req:

```
/req/uml-monitoring-feature-foi/foi
The target of the featureOfInterest property of the TimeseriesObservation shall be a MonitoringFeature type or a reference to an object of this type.
```

I propose dropping, folks can use MonitoringFeature, but also any other feature.
