Small cleanup of Query eXpander

src/metabase/db/metadata_queries.clj

src/metabase/driver.clj

src/metabase/driver/query_processor.clj

src/metabase/driver/query_processor/expand.clj

src/metabase/driver/query_processor/interface.clj

test/metabase/api/card_test.clj

test/metabase/api/dashboard_test.clj

test/metabase/api/dataset_test.clj

test/metabase/driver/query_processor_test.clj

test/metabase/test/data.clj