Remove references to SNAPSHOT builds

[gaul]

jclouds is out of compliance with ASF policies by advertising SNAPSHOT
builds to users.

[gaul]

Context:

Sorry, but the download page includes links to daily builds.
As the page itself points out, these are not official ASF releases.

As such, they must not be advertised on public download pages.
Such links should only be included on links intended for developers, not
the general public.

https://www.apache.org/dev/release-distribution#unreleased

Please fix the download page(s) and resubmit the announce email when this
has been done.

Thanks
Sebb
P.S. This was reported previously