fairy-slipper is retired, remove from releasenotes
fairy-slipper is retired, remove from releasenotes

Remove fairy-slipper from release-notes index file, it's now retired.

Change-Id: Ib2b54e2647629d1c822efaf6d95e80e414bb2c47

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