README.md: remove the reference to Google Container Engine

The referred document was removed in CL13622.

Change-Id: I71aaaf3e36cf18f66f1941e27ac76b3e7a6f24ca
Reviewed-on: https://upspin-review.googlesource.com/15300
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/README.md b/README.md
index ddc74f8..c8bc33f 100644
--- a/README.md
+++ b/README.md
@@ -9,9 +9,5 @@
 document for information about running an Upspin service that stores its data
 in Google Cloud Storage.
 
-See the [Deploying Upspin servers to Google Cloud Platform](https://upspin.io/doc/deploying_to_google_cloud.md)
-document for information about running an Upspin cluster on
-Google Container Engine.
-
 See the [master repository](https://github.com/upspin/upspin#readme)
 for more information about the Upspin project.