[Docker-maint] Bug#807294: golang-go: contains some but not all race-enabled packages

[Tianon Gravi]

> + # On linux/amd64 run.bash installs some race enabled standard library
> + # packages. Delete them again to avoid accidentally including them in
> + # the package.
> + rm -rf "$(GOROOT)/pkg/linux_amd64_race/"

This seems like the most correct solution to me, but I'm a little
confused about why we're hard-coding "linux_amd64" here -- shouldn't
this be "$(GOOS)_$(GOARCH)" so that it's whatever architecture we
build on?  Or perhaps "$(GOROOT)"/pkg/*_race/ ?

♥,
- Tianon
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