* 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
#include "atom/browser/browser.h"
#include <windows.h>  
#include <atlbase.h>
#include <shlobj.h>
#include <shobjidl.h>
#include "atom/browser/ui/win/jump_list.h"
#include "atom/common/atom_version.h"
#include "atom/common/native_mate_converters/string16_converter.h"
#include "base/base_paths.h"
#include "base/file_version_info.h"
#include "base/files/file_path.h"
#include "base/path_service.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "base/win/registry.h"
#include "base/win/win_util.h"
#include "base/win/windows_version.h"
namespace atom {
namespace {
const wchar_t kAppUserModelIDFormat[] = L"electron.app.$1";
BOOL CALLBACK WindowsEnumerationHandler(HWND hwnd, LPARAM param) {