scsi: Revert "target: iscsi: Wait for all commands to finish before freeing a session"

commit 807b9515 upstream.

Since commit e9d3009c introduced a regression and since the fix for
that regression was not perfect, revert this commit.

Link: https://marc.info/?l=target-devel&m=158157054906195


Cc: Rahul Kundu <rahul.kundu@chelsio.com>
Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Reported-by: Dakshaja Uppalapati <dakshaja@chelsio.com>
Fixes: e9d3009c ("scsi: target: iscsi: Wait for all commands to finish before freeing a session")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>