Remove unused arg `instances`

[Lawrance]

In function VolumeTableMixIn._set_id_if_nameless(), we define arg `instances`, but we never use it.

the codes snippet in file openstack_dashboard/dashboards/project/volumes/views.py：

def _set_id_if_nameless(self, volumes, instances):
        for volume in volumes:
            # It is possible to create a volume with no name through the
            # EC2 API, use the ID in those cases.
            if not volume.display_name:
                volume.display_name = volume.id

and should remove it to keep the code clean.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/66574
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=7f340ce40774e190fc5c89f7c8581c87e4559559
Submitter: Jenkins
Branch: master

commit 7f340ce40774e190fc5c89f7c8581c87e4559559
Author: lawrancejing <email address hidden>
Date: Tue Jan 14 21:55:02 2014 +0800

    Remove unused arg `instances`

    In function VolumeTableMixIn._set_id_if_nameless(), we
    define arg `instances`, but we never use it.

    Closes-Bug: #1269200

    Change-Id: Iac828511bfe8cd417a9c965d063c388fde73052e