[pkg-go] golang-github-hashicorp-serf is marked for autoremoval from testing

[Debian testing autoremoval watch]

golang-github-hashicorp-serf 0.8.1+git20180508.80ab4877~ds-1 is marked for autoremoval from testing on 2019-03-31

It (build-)depends on packages with these RC bugs:
922389: golang-protobuf-extensions: FTBFS (cannot find package "github.com/golang/protobuf/proto/testdata")