jbd2: remove t_checkpoint_io_list

Since t_checkpoint_io_list was stop using in jbd2_log_do_checkpoint()
now, it's time to remove the whole t_checkpoint_io_list logic.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230606135928.434610-3-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>