Revert "Update for latest RethinkDB"

Really sorry about this, it looks like it doesn't work. The 1.15 package depends on a version of libssl that isn't available in jessie. I tried experimenting with the precise and trusty packages, but they need a newer version of libprotobuf. It looks like there isn't a build of the 1.15 package that will actually work with jessie at this time. I didn't realize it wasn't working until after I proposed the merge request.