Removing some dead code.

Rx.NET/Source/System.Reactive.Core/Reactive/Concurrency/ConcurrencyAbstractionLayer.Default.cs

@@ -403,6 +403,7 @@ namespace System.Reactive.Concurrency
 #else
 using System;
 using System.Reactive.Disposables;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace System.Reactive.Concurrency
@@ -457,7 +458,7 @@ namespace System.Reactive.Concurrency
         
         public void Sleep(TimeSpan timeout)
         {
-            TaskHelpers.Delay(timeout).Wait();
+            TaskHelpers.Delay(timeout, CancellationToken.None).Wait();
         }
 
         public IStopwatch StartStopwatch()

Rx.NET/Source/System.Reactive.Core/Reactive/Concurrency/TaskHelpers.cs

@@ -10,11 +10,6 @@ namespace System.Reactive.Concurrency
     {
         private const int MAX_DELAY = int.MaxValue;
 
-        public static Task Delay(TimeSpan delay)
-        {
-            return Delay(delay, CancellationToken.None);
-        }
-
         public static Task Delay(TimeSpan delay, CancellationToken token)
         {
             var milliseconds = (long)delay.TotalMilliseconds;