message: Do not pass a placeholder user-agent string as a fallback when using WinHttp
  Verified the behavior is now as expected when telemetry policy is turned off.
  **Before:**
  ![image](https://user-images.githubusercontent.com/6527137/106042018-65d64e00-6091-11eb-8741-c6c42cb028d3.png)
  **After:**
  ![image](https://user-images.githubusercontent.com/6527137/106042157-86060d00-6091-11eb-9699-929128eb6ea1.png)
diff: @@ -189,7 +189,8 @@ void WinHttpTransport::CreateSessionHandle(std::unique_ptr<Details::HandleManage
  // Use WinHttpOpen to obtain a session handle.
  // The dwFlags is set to 0 - all WinHTTP functions are performed synchronously.
  handleManager->m_sessionHandle = WinHttpOpen(
  - L"WinHTTP Azure SDK",
  + NULL, // Do not use a fallback user-agent string, and only rely on the header within the
  + // request itself.
  WINHTTP_ACCESS_TYPE_NO_PROXY,
  WINHTTP_NO_PROXY_NAME,
  WINHTTP_NO_PROXY_BYPASS,
  