Remove inapplicable sentences from ICLA preamble.

* modules/openstack_project/files/gerrit/cla.html: As was pointed
out on the openstack-dev mailing list by Zane Bitter, the last
several sentences of the first paragraph of the preamble no longer
apply to the new signing process. This change removes them from the
text. For discussion, see...

    http://lists.openstack.org/pipermail/openstack-dev/2013-March/006189.html

Change-Id: Iceadd57e5008f2289fb5e5c546a40f0f9ededc7c
Reviewed-on: https://review.openstack.org/23455
Reviewed-by: Jonathan Bryce <jbryce@jbryce.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins