Reduce race between LUN destruction and request arrival.

MFC after:	1 week
Ticket:		#6721

(cherry picked from commit abdf50c824fc0ca0785577f92d87fc93914ff64d)
Remove bunch of unused lun variables.

MFC after:	1 week

(cherry picked from commit 2aadb1a5367b1b0d1a92611bab505d6a069a2e42)