db/del -> db/delete!

src/metabase/api/session.clj

src/metabase/db.clj

src/metabase/db/migrations.clj

src/metabase/models/setting.clj

test/metabase/api/revision_test.clj

test/metabase/api/session_test.clj

test/metabase/events/revision_test.clj