doc: remove template use in godebug.md

This file used to be implicitly a template prior to CL 733500, but now
it's no longer a template. The only template use here can be trivially
expressed with pure Markdown syntax, so do that. (The alternative path
would be to set 'template: true' explicitly.)

Fixes #78211.

Change-Id: I66970f0d081b4e80e8d330330ad17a5702364391
Reviewed-on: https://go-review.googlesource.com/c/go/+/756560
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>