Remove "buy from lulu" references from from the Security Guide landing page
Remove "buy from lulu" references from from the Security Guide landing page

Change-Id: I050edbb307aef4bf0ce7ccba1ce95c3e65c487d6
Closes-bug: #1576369

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals