Delete the placeholder file: example.rst

example.rst was a placeholder, because we needed specs/kilo to
exist for people submitting specs. Now that we have an approved spec,
the kilo directory exists.

See https://review.openstack.org/127047 for more information as to
why example.rst was there in the first place.

Change-Id: Ic062d265dce75e284c47ad90d2adb4cdca6134f0