Remove the ability to use @GeoPointBinding on properties of type GeoPoint

The point (ha!) of @GeoPointBinding is to handle complex cases where reflection must be used to access the latitude and longitude.

For simpler cases where the property implements GeoPoint, the much simpler @GenericField should be used.

Let's make sure people don't start using @GeoPointBinding everywhere for no reason, this might come and bite us at some point.