remove unnecessary assertion

Author: liveans

src/libraries/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpRequestCallback.cs

@@ -234,7 +234,6 @@ private static void OnRequestRedirect(WinHttpRequestState state, Uri redirectUri
         private static void OnRequestSendingRequest(WinHttpRequestState state)
         {
             Debug.Assert(state != null, "OnRequestSendingRequest: state is null");
-            Debug.Assert(state.RequestHandle != null, "OnRequestSendingRequest: state.RequestHandle is null");
             Debug.Assert(state.RequestMessage != null, "OnRequestSendingRequest: state.RequestMessage is null");
             Debug.Assert(state.RequestMessage.RequestUri != null, "OnRequestSendingRequest: state.RequestMessage.RequestUri is null");