libgo: don't put golang.org packages in zstdpkglist.go

This ensures that internal/goroot.IsStandardPackage does not treat
golang.org packages as being in the standard library.

For golang/go#41368
Fixes golang/go#41499

Change-Id: I58abc84c6c8544b3d7f513bda7a5e5a63d0a9937
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/256319
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
2 files changed