doc: make use of simpler symbol links for relnotes
This is a practical use of CL 577915, follow-up to CL 577835.
Change-Id: Ibe7e2fa11b444afa1898dc6f6aba1512fe98f1fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/578195 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Jonathan Amsterdam <jba@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>