remove Cards when a Database is deleted. this now allows a Database to be...

remove Cards when a Database is deleted.  this now allows a Database to be deleted at any time without failing on an FK error from the database.

src/metabase/models/database.clj

@@ -31,6 +31,7 @@
         :tables (delay (sel :many 'metabase.models.table/Table :db_id id :active true (order :display_name :ASC))))))
 
   (pre-cascade-delete [_ {:keys [id] :as database}]
+    (cascade-delete 'metabase.models.card/Card :database_id id)
     (cascade-delete 'metabase.models.table/Table :db_id id)))
 
 (extend-ICanReadWrite DatabaseEntity :read :always, :write :superuser)