Avoid module on binary

[Tatskaari]

This was causing issues with go_binary rules generated in go_repos:

➜  please git:(update-plugins) plz build ///third_party/go/github.com_googlecodelabs_tools_claat//:claat
Build stopped after 30ms. 1 target failed:
    ///third_party/go/github.com_googlecodelabs_tools_claat//:claat
plz-out/subrepos/third_party/go/github.com_googlecodelabs_tools_claat/BUILD:3:1: error: Unknown argument to go_binary: _module

go_binary(
^
    name = "claat",

[izissise]

I think a got a bug because of this,it was really hard to track down

with

go_repo(
    module="gitlab.com/nbdkit/nbdkit/plugins/golang/src/libguestfs.org/nbdkit",
    version="712fe24c18df21567e566a013d92f9138666ec8c",
    install=["nbdkit"],
)

I get

cgo_library(
    name = "nbdkit",
    srcs = [
        "nbdkit.go",
        "utils.go",
        "wrappers.go",
    ],
    hdrs = ["wrappers.h"],
    _module = "gitlab.com/nbdkit/nbdkit/plugins/golang/src/libguestfs.org/nbdkit@712fe24c18df21567e566a013d92f9138666ec8c",
    go_srcs = [],
    linker_flags = ["-Wl,--unresolved-symbols=ignore-in-object-files"],
    visibility = ["PUBLIC"],
)

and
error: Unknown argument to cgo_library: _module