target/user: Don't free expired command when time out

target/user: Don't free expired command when time out

Which would result in NPE after when userspace connected again.

Expired command would be freed either when handling command(by userspace),
or when device was tearing down

Reviewed-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Sheng Yang <sheng@yasker.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Orabug: 25395066
(cherry picked from commit b25c786399367b9a8bd955d8496669d019409bec)
Signed-off-by: Kyle Fortin <kyle.fortin@oracle.com>
Reviewed-by: Shan Hai <shan.hai@oracle.com>