Update 404 page
Update 404 page

It's now one year that we announce major rework - remove that statement.
If people hit 404s, it should be reported against the projects itself.

Change-Id: I201cd2267d3e77ad39375ebeca14649cf5631eba

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals