[development] Let's kill $user->data

Hi, Two steps a) We remove $user->data handling code from D6 core. No save, no load. New installs won't have this column. b) D7 will drop the $user->data if it exists. (SELECT * FROM user, $account = db_fetch_array, if(isset($account['data'])) -- no need for DDL to check for a column). This way D6 contribs can clean up $user->data and migrate to their own tables. Regards NK