MB-6972:  new public V3 key. Lost previous private key that goes with.

Private key is now safe in build_private repo.  See:

https://github.com/couchbase/build_private/blob/master/keys/linux_repo/couchbase-server-private-key-v3.gpg

Change-Id: I0e4292d3d89f229d61c0186228b200b2610a0cc9