golang-go.crypto is in xenial-proposed and the build certainly should have used it (and reports so, if only Built-Using can be trusted). If that's not the case, it's definitely a bug that needs to be fixed.
However, we need to consider this separately from yakkety. golang-go.crypto in yakkety should be removed, as it currently breaks other things in the archive (with this package, other golang packages will be uninstallable) and blocks other SRUs from being verified.
golang-go.crypto is in xenial-proposed and the build certainly should have used it (and reports so, if only Built-Using can be trusted). If that's not the case, it's definitely a bug that needs to be fixed.
However, we need to consider this separately from yakkety. golang-go.crypto in yakkety should be removed, as it currently breaks other things in the archive (with this package, other golang packages will be uninstallable) and blocks other SRUs from being verified.