Fix publishing of API Reference

We are publishing at api.openstack.org top-level but the job
is copying to an api-ref subdirectory. Changing the Jenkins setup is the
better solution here than copying directly into publish-docs - it would
create a more complex script.

Remove macro upload-to-api-site and add the publisher directly to the
openstack-api-ref job since this is an exception from the other rules -
and this is the only job publishing to api.o.o.

Change-Id: Ib5511ed7cbf8dfc90cb42e295fe68f39aa1e0a8f