scsi: iscsi: Remove unused extern declaration iscsi_lookup_iface()

This is not used anymore and can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20230725141531.10424-1-yuehaibing@huawei.com


Reviewed-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>