target: Drop incorrect se_lun_acl release for dynamic -> explict ACL conversion

This patch removes some potentially problematic legacy code within
core_clear_initiator_node_from_tpg() that was originally intended to
release left over se_lun_acl setup during dynamic NodeACL+MappedLUN
generate when running with TPG demo-mode operation.

Since we now only ever expect to allocate and release se_lun_acl from
within target_core_fabric_configfs.c:target_fabric_make_mappedlun() and
target_fabric_drop_mappedlun() context respectively, this code for
demo-mode release is incorrect and needs to be removed.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>