jbd2: remove wrong sb->s_sequence check

Journal emptiness is not determined by sb->s_sequence == 0 but rather by
sb->s_start == 0 (which is set a few lines above). Furthermore 0 is a
valid transaction ID so the check can spuriously trigger. Remove the
invalid WARN_ON.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250206094657.20865-3-jack@suse.cz


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