jbd2: remove unused 'JBD2_CHECKPOINT_IO_ERROR' and 'j_atomic_flags'

Since 'JBD2_CHECKPOINT_IO_ERROR' and j_atomic_flags' are not useful
anymore after fs dev's errseq is imported into jbd2, just remove them.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231213013224.2100050-4-chengzhihao1@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>