[System]: In 'WebConnection.EndWrite()': always call EndWrite() on the underlying socket.

(cherry picked from commit dd9d66a7c28ba77bf5ef7e4d7f6cb60ca3feb5a9)

mcs/class/System/System.Net/WebConnection.cs

@@ -992,9 +992,6 @@ namespace System.Net
 
 		internal bool EndWrite (HttpWebRequest request, bool throwOnError, IAsyncResult result)
 		{
-			if (request.FinishedReading)
-				return true;
-
 			Stream s = null;
 			lock (this) {
 				if (status == WebExceptionStatus.RequestCanceled)