scsi: Revert "target/core: Inline transport_lun_remove_cmd()"

scsi: Revert "target/core: Inline transport_lun_remove_cmd()"

Commit 34aca3042c0a postponed the percpu_ref_put(&se_cmd->se_lun->lun_ref)
call from command completion to the time when the final command reference
is dropped. That approach is not compatible with the iSCSI target driver
because the iSCSI target driver keeps the command with the highest stat_sn
after it has completed until the next command is received (see also
iscsit_ack_from_expstatsn()). Fix this regression by reverting commit
34aca3042c0a.

Fixes: 34aca3042c0a ("scsi: target/core: Inline transport_lun_remove_cmd()")
Cc: Pavel Zakharov <pavel.zakharov@delphix.com>
Cc: Mike Christie <mchristi@redhat.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200210051202.12934-1-bvanassche@acm.org
Reported-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>