_content/ref: specify redirect for /ref and /ref/ using /ref/index.md

We want both `/ref` and `/ref/` to point to `/doc/#references` section.
All documents for /ref/* are available from this unified website, so we
can set up a redirect rule using the native redirect support provided by
the internal/web package instead of relying on the internal/redirect rule.

Fixes golang/go#53243

Change-Id: Ibed1aefc82f8b93ae14775efbb456b1571053eda
Reviewed-on: https://go-review.googlesource.com/c/website/+/413914
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>

_content/ref/index.md

@@ -0,0 +1,3 @@
+<!--{
+	"Redirect": "/doc/#references"
+}-->

cmd/golangorg/testdata/web.txt

@@ -422,3 +422,9 @@ redirect == https://go.dev/dl/?mode=json
 GET https://go.dev/dl/?mode=json
 body contains .windows-amd64.msi
 body !contains UA-
+
+GET https://go.dev/ref
+redirect == /doc/#references
+
+GET https://go.dev/ref/
+redirect == /doc/#references

internal/redirect/redirect.go

@@ -106,12 +106,6 @@ var redirects = map[string]string{
 	"/issues":     "https://github.com/golang/go/issues",
 	"/design":     "https://go.googlesource.com/proposal/+/master/design",
 
-	// In Go 1.2 the references page is part of /doc/.
-	"/ref": "/doc/#references",
-	// This next rule clobbers /ref/spec and /ref/mem.
-	// TODO(adg): figure out what to do here, if anything.
-	// "/ref/": "/doc/#references",
-
 	// Be nice to people who are looking in the wrong place.
 	"/pkg/C/":   "/cmd/cgo/",
 	"/doc/mem":  "/ref/mem",

internal/redirect/redirect_test.go

@@ -22,7 +22,6 @@ func errorResult(status int) redirectResult {
 func TestRedirects(t *testing.T) {
 	var tests = map[string]redirectResult{
 		"/build":                         {301, "https://build.golang.org"},
-		"/ref":                           {301, "/doc/#references"},
 		"/doc/mem":                       {301, "/ref/mem"},
 		"/doc/spec":                      {301, "/ref/spec"},
 		"/foo":                           errorResult(404),