block, bfq: remove blkg_path()

After commit 35fe6d76 ("block: use standard blktrace API to output
cgroup info for debug notes"), the field 'bfqg->blkg_path' is not used
and hence can be removed, and therefor blkg_path() is not used anymore
and can be removed.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240618032753.3502528-1-yukuai1@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>