[SCSI] iscsi update: rm conn lock

>From erezz@voltaire.com:

rm conn->lock since it is not used anymore. The dataqueue is protected
by the session lock and xmitmutex.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Alex Aizman <itn780@yahoo.com>
Signed-off-by: Dmitry Yusupov <dmitry_yus@yahoo.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>