[Sync] Remove DropAttachments from AttachmentService and SyncData

sync/api/sync_data.h

 // Copyright 2012 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.
 
 #ifndef SYNC_API_SYNC_DATA_H_
 #define SYNC_API_SYNC_DATA_H_
 
 #include <iosfwd>
 #include <string>
 #include <vector>
@@ skipping 172 matching lines @@
   //
   // |callback| will be invoked when the operation is complete (successfully
   // or otherwise).
   //
   // Retrieving the requested attachments may require reading local storage or
   // requesting the attachments from the network.
   //
   void GetOrDownloadAttachments(
       const AttachmentIdList& attachment_ids,
       const AttachmentService::GetOrDownloadCallback& callback);
-
-  // Drop (delete from local storage) the attachments associated with this
-  // SyncData specified in |attachment_ids|. This method will not delete
-  // attachments from the server.
-  //
-  // |callback| will be invoked when the operation is complete (successfully
-  // or otherwise).
-  void DropAttachments(const AttachmentIdList& attachment_ids,
-                       const AttachmentService::DropCallback& callback);
 };
 
 // gmock printer helper.
 void PrintTo(const SyncData& sync_data, std::ostream* os);
 
 typedef std::vector<SyncData> SyncDataList;
 
 }  // namespace syncer
 
 #endif  // SYNC_API_SYNC_DATA_H_