eliminated more dead code.  Removed useless wrapper functions in fof-main.php, replaced them with their equivalents in fof-db.php

removed useless wrapper functions

fof_is_subscribed -> fof_db_is_subscribed
fof_mark_unread -> null.  Was never used anyway
fof_mark_read -> null.  Was never used
fof_get_unread_count -> fof_db_get_unread_count
actually deleted the dead code, instead of just commenting out