Feat: allow user to select no real-time weather data

[Rudd-O]

The weather station that the integration asks about when configuring, does not necessarily have to be used. In other words, it should be optional. #4 hints at this.

If the user selects no weather station (which should be a possibility), then the sensor entities that depend on this weather station being configured should simply not be added to Home Assistant.

Stretch goal: if the entities already exist for whatever reason, simply delete them. Not sure how to do this!

[Rudd-O]

Fixed in b4685f9 .