Removing extraneous call to IHttpClient.Initialize (#3830)

An extraneous call to IHttpClient.Initialize when sending the start requests resets httpClients in the DefaultHttpClient. This may break load balancers and prevent reusing HTTPS connections (SSL negotation will happen twice - once for negotiate and once for start)

More: #3829

src/Microsoft.AspNet.SignalR.Client/Transports/TransportHelper.cs

@@ -57,8 +57,6 @@ public virtual Task<string> GetStartResponse(IHttpClient httpClient, IConnection
 
             var startUrl = UrlBuilder.BuildStart(connection, transport, connectionData);
 
-            httpClient.Initialize(connection);
-
             return httpClient.Get(startUrl, connection.PrepareRequest, isLongRunning: false)
                             .Then(response => response.ReadAsString());
         }