Remove useless codes for server_group

[wingwj]

Some codes about 'extract_members' from 'create_server_group' is written in original bp/patch's reviewing (https://review.openstack.org/#/c/62557/29).

But as the design variation, it can't be specified members in create API (see it in PS29 vs PS30).
But some codes are still kept after this feature merged.
So it's necessary to remove them.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/96998

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/96998
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=897a4b754daae840100e63433d928bb62a81fbdc
Submitter: Jenkins
Branch: master

commit 897a4b754daae840100e63433d928bb62a81fbdc
Author: wingwj <email address hidden>
Date: Sat May 31 11:17:12 2014 +0800

    Remove useless codes for server_group

    Some codes about 'extract_members' from 'create_server_group'
    is written in original bp/patch's reviewing
    (I650a8f191dea5eab5b4b1828f0b9f65e33edea2a).

    But as the design variation, it can't be specified members
    in create API (see it in PS29 vs PS30).
    But some useless codes are still kept after this feature merged.
    So it's necessary to remove them.

    Change-Id: I087c8389f2c735a36d656b44c6a3ecfe3a4aa5a3
    Closes-Bug: #1325148