* 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
if (app_user_model_id_.empty()) {
    SetAppUserModelID(base::ReplaceStringPlaceholders(
        kAppUserModelIDFormat, base::UTF8ToUTF16(GetName()), nullptr));
  }
  return app_user_model_id_.c_str();
}
std::string Browser::GetExecutableFileVersion() const {
  base::FilePath path;
  if (PathService::Get(base::FILE_EXE, &path)) {
    std::unique_ptr<FileVersionInfo> version_info(
        FileVersionInfo::CreateFileVersionInfo(path));
    return base::UTF16ToUTF8(version_info->product_version());
  }
  return ATOM_VERSION_STRING;
}
std::string Browser::GetExecutableFileProductName() const {
  base::FilePath path;
  if (PathService::Get(base::FILE_EXE, &path)) {
    std::unique_ptr<FileVersionInfo> version_info(
        FileVersionInfo::CreateFileVersionInfo(path));
    return base::UTF16ToUTF8(version_info->product_name());
  }
  return ATOM_PRODUCT_NAME;
}
}