[#47380499] Sql Tasks no longer return their execution schema
[#47380499] remove the pass-through SqlExecutor module

Conflicts:
	app/controllers/previews_controller.rb
	spec/controllers/previews_controller_spec.rb
[#47380499] Clean up cancelable_query statements left after streaming.  Expand test coverage.
[#47380499] CancelableQuery@@running_statements use java ConcurrentHashMap