Remove connector properties from descriptors on the /connector-types response

After DBZ-3255 is done we can remove the `properties` field from the connector type descriptors.
Future versions will only get the list of available connectors (id, name, class, enabled/disabled status, etc) from the `/connector-types` endpdoint.
Connector properties will be served per connector-type-id from the `/connector-types/{connector-type-id}` endpoint.