target: remove ->put_session method

The only instance of ->put_session is in qla2xxx, and was added by commit
aaf68b ("tcm_qla2xxx: Convert to TFO->put_session() usage") with the following
description:

    This patch converts tcm_qla2xxx code to use an internal kref_put() for
    se_session->sess_kref in order to ensure that qla_hw_data->hardware_lock
    can be held while calling qlt_unreg_sess() for the final put.

But these day we're already holding the hardware lock over qlt_unreg_sess in
the ->close_session callback, so we're fine without this method.

(Re-add missing tcm_qla2xxx_release_session + drop put_session usage - nab)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>