index: remove dead links Fixes golang/go#72839 Change-Id: I18a12716e7040c7ba64570b8162a9052b205d2ba Reviewed-on: https://go-review.googlesource.com/c/wiki/+/657555 Commit-Queue: Ian Lance Taylor <iant@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Auto-Submit: Ian Lance Taylor <iant@golang.org>