[release-branch.go1.7] doc/devel/release.html: document go1.6.3 doesn't actually support macOS Sierra

Updates #17824.

Change-Id: I73cf89c21b418158c7014c3271cd1103a17a5c86
Reviewed-on: https://go-review.googlesource.com/32882
Reviewed-by: Brad Fitzpatrick <[email protected]>
Reviewed-on: https://go-review.googlesource.com/32885
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Minux Ma <[email protected]>

Author: minux

doc/devel/release.html

@@ -89,7 +89,7 @@ <h3 id="go1.6.minor">Minor revisions</h3>
 <p>
 go1.6.3 (released 2016/07/17) includes security fixes to the
 <code>net/http/cgi</code> package and <code>net/http</code> package when used in
-a CGI environment. This release also adds support for macOS Sierra.
+a CGI environment.
 See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.6.3">Go
 1.6.3 milestone</a> on our issue tracker for details.
 </p>