[Storm SQL] Drop Aggregate & Join support on Trident mode

This was already discussed on dev@ mailing list. [1]

As aggregation and join don't make sense for streaming without windowing, we're not ready to handle them on SQL semantic. Unless we're ready, it would be better to drop them to not making any confusions. (Aggregation and join on Trident semantic could be different from what users expect.)

[1] http://mail-archives.apache.org/mod_mbox/storm-dev/201610.mbox/%3CCAF5108hNLfSJq+pUvD_RRMtGKmrGV7yQSwqn3j8dA9SaN6HcMg@mail.gmail.com%3E