Reset rel-2.5.1.xml to 2.5.1 GA for a test build using R16 on Windows

Change-Id: I9bb0994021469f7beae9dd67415c194158b37a0e
Reviewed-on: http://review.couchbase.org/42562
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>