def delete(cv)
      @executor.transact do |dbh|
        sth = dbh.prepare(DELETE_STMT)
        delete_recursive(cv, sth)
        sth.finish
      end
    end
def delete(cv)
      @executor.transact do |dbh|
        sth = dbh.prepare(DELETE_STMT)
        delete_recursive(cv, sth)
        sth.finish
      end
    end
Deletes the given ControlledValue record in the database. Recursively deletes the
 transitive closure of children as well.

 @param [ControlledValue] cv the controlled value to delete