internal/backport: delete

Now that the deploy happens with Go 1.19, it's viable to start using
these packages from the standard library instead of their backported
temporary copies.

Keeping Go 1.18 happy during its last two months of support requires
a tiny complication in pkgdoc package. An alternative path is to not
drop internal/backport/go/doc and all of its dependencies right away,
but getting to zero backported packages sooner was hard to resist...

For golang/go#51800.

Change-Id: Ieb7a137a033d6b6850dfc019c8c0c767756cc30d
Reviewed-on: https://go-review.googlesource.com/c/website/+/456522
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

cmd/golangorg/server.go

@@ -14,6 +14,8 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"go/format"
+	"html/template"
 	"io/fs"
 	"io/ioutil"
 	"log"
@@ -31,8 +33,6 @@ import (
 	"cloud.google.com/go/datastore"
 	"golang.org/x/build/repos"
 	"golang.org/x/website"
-	"golang.org/x/website/internal/backport/go/format"
-	"golang.org/x/website/internal/backport/html/template"
 	"golang.org/x/website/internal/blog"
 	"golang.org/x/website/internal/codewalk"
 	"golang.org/x/website/internal/dl"

cmd/googlegolangorg/main.go

@@ -3,11 +3,10 @@ package main
 
 import (
 	"fmt"
+	"html/template"
 	"net/http"
 	"os"
 	"strings"
-
-	"golang.org/x/website/internal/backport/html/template"
 )
 
 var repoMap = map[string]*repoImport{

internal/api/api_test.go

@@ -5,11 +5,10 @@
 package api
 
 import (
+	"go/build"
 	"os"
 	"runtime"
 	"testing"
-
-	"golang.org/x/website/internal/backport/go/build"
 )
 
 func TestParseVersionRow(t *testing.T) {