oauth2: remove stale comment

Change-Id: If9fba85ac8b20545cee54cafe1c7672880acf498
Reviewed-on: https://go-review.googlesource.com/4391
Reviewed-by: Burcu Dogan <jbd@google.com>
diff --git a/google/google.go b/google/google.go
index bbe6a38..473e862 100644
--- a/google/google.go
+++ b/google/google.go
@@ -25,9 +25,6 @@
 	"google.golang.org/cloud/compute/metadata"
 )
 
-// TODO(bradfitz,jbd): import "google.golang.org/cloud/compute/metadata" instead of
-// the metaClient and metadata.google.internal stuff below.
-
 // Endpoint is Google's OAuth 2.0 endpoint.
 var Endpoint = oauth2.Endpoint{
 	AuthURL:  "https://accounts.google.com/o/oauth2/auth",