* 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
mate::Arguments* args) {
  if (protocol.empty())
    return false;
  base::string16 exe;
  if (!GetProtocolLaunchPath(args, &exe))
    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;
  base::win::RegKey commandKey;
  if (FAILED(key.Open(root, keyPath.c_str(), KEY_ALL_ACCESS)))
    
    return false;
  if (FAILED(commandKey.Open(root, cmdPath.c_str(), KEY_ALL_ACCESS)))
    
    return false;
  base::string16 keyVal;
  if (FAILED(commandKey.ReadValue(L"", &keyVal)))
    
    return false;
  
  return keyVal == exe;
}
bool Browser::SetBadgeCount(int count) {