ext4: remove unused parameter biop in ext4_issue_discard()

all caller of ext4_issue_discard() would set biop to NULL since
'commit 55cdd0af

 ("ext4: get discard out of jbd2 commit kthread
contex")', it's unnecessary to keep this parameter any more.

Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/20240226081731.3224470-1-haowenchao2@huawei.com


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