doc: remove mention of defunct golang-bugs mailing list

Fixes #12299

Change-Id: Id7b73d2935c9f7c0952f833613973ef455d02b0d
Reviewed-on: https://go-review.googlesource.com/13858Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/contrib.html

@@ -67,9 +67,6 @@ href="https://groups.google.com/group/golang-nuts">golang-nuts</a>.</p>
 <h3 id="golang-checkins"><a href="https://groups.google.com/group/golang-checkins">Checkins Mailing List</a></h3>
 <p>A mailing list that receives a message summarizing each checkin to the Go repository.</p>
 
-<h3 id="golang-bugs"><a href="https://groups.google.com/group/golang-bugs">Bugs Mailing List</a></h3>
-<p>A mailing list that receives each update to the Go <a href="//golang.org/issue">issue tracker</a>.</p>
-
 <h3 id="build_status"><a href="//build.golang.org/">Build Status</a></h3>
 <p>View the status of Go builds across the supported operating
 systems and architectures.</p>