cmd/go: remove unused var BuildToolchainLinker and BuildToolchainCompiler
Change-Id: I4bb855f6ada5c550a46f69313a2f47631bf657ca
GitHub-Last-Rev:
2af07f9d7bda0de31b61d434635cd1c2c568af06
GitHub-Pull-Request: golang/go#65838
Reviewed-on: https://go-review.googlesource.com/c/go/+/565517
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>