jbd2: remove stale comment of update_t_max_wait

Commit 2d442920 ("jbd2: remove CONFIG_JBD2_DEBUG to update
t_max_wait") removed jbd2_journal_enable_debug, just remove stale comment
about jbd2_journal_enable_debug.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250123155014.2097920-5-shikemeng@huaweicloud.com


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