ksmbd: remove unused ksmbd_file_table_flush function

mainline inclusion
from mainline-5.15-rc1
commit 687c59e7
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/687c59e702f4



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ksmbd_file_table_flush is a leftover from SMB1. This function is no longer
needed as SMB1 has been removed from ksmbd.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>