Do not create unused properties

[klahnakoski]

The current schema management will ensure all indexes, under one alias, have the same properties; adding missing ones if necessary:

https://github.com/mozilla/ActiveData/blob/ceb0109b17e3c670ef563bd02e22ac5943a9c2fe/vendor/jx_elasticsearch/meta.py#L130

We must have a way to prevent the creation of columns when cardinality==0 so unused properties eventually disappear.