jbd2: remove jbd2_journal_unfile_buffer()

Since the function jbd2_journal_unfile_buffer() is no longer called
anywhere after commit e5a120ae ("jbd2: remove journal_head from
descriptor buffers"), so let's remove it.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250306063240.157884-1-libaokun@huaweicloud.com


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