doc: Remove outdated admin_UFO.md

Remove outdated admin_UFO.md file and add file to point to upstream
SwiftOnFile repo and documentation.

Change-Id: I87e17c11197e0ed3dd9f10a3ace88c2b3c23566e
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/8543
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Tested-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>