cmd/release: remove the blog from the releases

This removes the blog from the release binary, greatly lowering the size
of each release. It will now redirect to blog.golang.org, unless the user
runs "go get -u golang.org/x/blog" to cache it locally, in which case the
release-shipped godoc will prefer the local copy of the blog.

Currently, the blog is growing at ~2MB a year, thus including the blog in
every new go version release will continue to grow the releases over time.

The release size was 170MB for go1.11rc1, this change reduces the size
by 34MB, a 20% reduction.

Fixes golang/go#21917

Change-Id: I53bf0c416c2085da10b6bb70f8aa6cae8e826dc3
Reviewed-on: https://go-review.googlesource.com/130575
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/cmd/release/release.go b/cmd/release/release.go
index 9dd48a4..ceefca3 100644
--- a/cmd/release/release.go
+++ b/cmd/release/release.go
@@ -40,7 +40,6 @@
 	rev       = flag.String("rev", "", "Go revision to build")
 	toolsRev  = flag.String("tools", "", "Tools revision to build")
 	tourRev   = flag.String("tour", "master", "Tour revision to include")
-	blogRev   = flag.String("blog", "master", "Blog revision to include")
 	netRev    = flag.String("net", "master", "Net revision to include")
 	version   = flag.String("version", "", "Version string (go1.5.2)")
 	user      = flag.String("user", username(), "coordinator username, appended to 'user-'")
@@ -239,7 +238,6 @@
 
 const (
 	toolsRepo = "golang.org/x/tools"
-	blogRepo  = "golang.org/x/blog"
 	tourRepo  = "golang.org/x/tour"
 )
 
@@ -307,7 +305,6 @@
 	}{
 		{"go", *rev},
 		{"tools", *toolsRev},
-		{"blog", *blogRev},
 		{"tour", *tourRev},
 		{"net", *netRev},
 	} {
diff --git a/cmd/release/releaselet.go b/cmd/release/releaselet.go
index d08d15e..7899dd3 100644
--- a/cmd/release/releaselet.go
+++ b/cmd/release/releaselet.go
@@ -36,9 +36,6 @@
 	if err := godoc(); err != nil {
 		log.Fatal(err)
 	}
-	if err := blog(); err != nil {
-		log.Fatal(err)
-	}
 	if err := tour(); err != nil {
 		log.Fatal(err)
 	}
@@ -96,20 +93,6 @@
 	)
 }
 
-const blogPath = "golang.org/x/blog"
-
-var blogContent = []string{
-	"content",
-	"template",
-}
-
-func blog() error {
-	// Copy blog content to $GOROOT/blog.
-	blogSrc := filepath.Join("gopath/src", blogPath)
-	contentDir := filepath.FromSlash("go/blog")
-	return cpAllDir(contentDir, blogSrc, blogContent...)
-}
-
 const tourPath = "golang.org/x/tour"
 
 var tourContent = []string{