[release-branch.go1.24] cmd/go: remove user-content from doc strings in cgo ASTs.

[release-branch.go1.24] cmd/go: remove user-content from doc strings in cgo ASTs.

Thank you to RyotaK (https://ryotak.net) of GMO Flatt Security Inc. for reporting this issue.

Updates #76697
Fixes #77128
Fixes CVE-2025-61732

Change-Id: Ie2a96b79a813e362cbf8e6cb0e3c2d0c022bcb29
Reviewed-on: https://go-review.googlesource.com/c/go/+/740001
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>