Revert of Keep track of which attachments are referenced by which sync entries.

sync/internal_api/public/base/attachment_id_proto.cc

Index: sync/internal_api/public/base/attachment_id_proto.cc
diff --git a/sync/internal_api/public/base/attachment_id_proto.cc b/sync/internal_api/public/base/attachment_id_proto.cc
deleted file mode 100644
index d09c83e9567d75e33d5a422969249c499441c775..0000000000000000000000000000000000000000
--- a/sync/internal_api/public/base/attachment_id_proto.cc
+++ /dev/null
@@ -1,19 +0,0 @@
-// 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.
-
-#include "sync/internal_api/public/base/attachment_id_proto.h"
-
-#include "base/rand_util.h"
-
-namespace syncer {
-
-sync_pb::AttachmentIdProto CreateAttachmentIdProto() {
-  // Only requirement here is that this id must be globally unique.
-  // TODO(maniscalco): Consider making this base64 encoded.
-  sync_pb::AttachmentIdProto proto;
-  proto.set_unique_id(base::RandBytesAsString(16));
-  return proto;
-}
-
-}  // namespace syncer