* Electron version: 1.7.x
* Operating system: Windows

### Expected behavior
removeAsDefaultProtocolClient should also delete the protocol key - HKCU\Software\Classes\#protocol#

### Actual behavior
removeAsDefaultProtocolClient doesn't delete the protocol key - HKCU\Software\Classes\#protocol#

### How to reproduce
Call app.setAsDefaultProtocolClient('foo') and app.removeAsDefaultProtocolClient('foo'). HKCU\Software\Classes\foo stay in the registry for windows.
atom/browser/browser_win.cc
JumpList jump_list(GetAppUserModelID());
  if (!jump_list.Begin())
    return false;
  JumpListCategory category;
  category.type = JumpListCategory::Type::TASKS;
  category.items.reserve(tasks.size());
  JumpListItem item;
  item.type = JumpListItem::Type::TASK;
  for (const auto& task : tasks) {
    item.title = task.title;
    item.path = task.program;
    item.arguments = task.arguments;
    item.icon_path = task.icon_path;
    item.icon_index = task.icon_index;
    item.description = task.description;
    category.items.push_back(item);
  }
  jump_list.AppendCategory(category);
  return jump_list.Commit();
}
bool Browser::RemoveAsDefaultProtocolClient(const std::string& protocol,
                                            mate::Arguments* args) {
  if (protocol.empty())
    return false;
  
  HKEY root = HKEY_CURRENT_USER;
  base::string16 keyPath = base::UTF8ToUTF16("Software\\Classes\\" + protocol);
  
  base::string16 cmdPath = keyPath + L"\\shell\\open\\command";
  base::win::RegKey key;