[SCSI] libfc: removes unused disc_work and ex_list

Reported-by: Alex Lyakas <alexl@mellanox.co.il>
Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>