cmd/go: link to go.dev/doc/godebug for removed GODEBUG settings
This makes the user experience better, before users would receive
an unknown godebug error message, now we explicitly mention that
it was removed and link to go.dev/doc/godebug where users can find
more information about the removal.
Additionally we keep all the removed GODEBUGs in the source, making
sure we do not reuse such GODEBUG after it is removed.
Updates #72111
Updates #75316
Change-Id: I6a6a6964cce1c100108fdba4bfba7d13cd9a893a
Reviewed-on: https://go-review.googlesource.com/c/go/+/701875 Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Mateusz Poliwczak <mpoliwczak34@gmail.com> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Michael Matloob <matloob@google.com>