[release-branch.go1.14] doc/go1.14: crypto/tls.Config.NameToCertificate is deprecated

Also crypto/tls.Config.BuildNameToCertificate.

Note that this field and method were deprecated in the Go 1.14 release,
so this change is to the 1.14 release notes.

For #37626
Fixes #38030

Change-Id: If8549bc746f42a93f1903439e1b464b3e81e2c19
Reviewed-on: https://go-review.googlesource.com/c/go/+/240005


Reviewed-by: Filippo Valsorda <filippo@golang.org>
(cherry picked from commit 186e61f3)
Reviewed-on: https://go-review.googlesource.com/c/go/+/240011