Revert of Bring up of the enhanced bookmarks cluster service.

components/enhanced_bookmarks/proto/cluster.proto

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-//
-syntax = "proto2";
-option optimize_for = LITE_RUNTIME;
-
-package image_collections;
-
-message ClusterRequest {
-  // Optional list of docs we want to cluster--a subset of the user's available
-  // docs.
-  repeated string docs = 1;
-
-  // When docs is empty, used to determine which clips are clustered.  If set to
-  // true, cluster all the user's clips.  Otherwise (default) cluster all of the
-  // user's uncategorized clips.
-  optional bool cluster_all = 3 [default = false];
-
-  extensions 2;
-}
-
-message ClusterResponse {
-  message Cluster {
-    repeated string docs = 1;
-    // May be empty or unset if no reasonable title could be found.
-    optional string title = 2;
-  }
-
-  // Each of ClusterRequest.docs will exist in exactly one cluster. Some
-  // clusters may be singletons, so
-  //   ClusterResponse.clusters_size() <= ClusterRequest.docs_size().
-  repeated Cluster clusters = 1;
-}