Clean up some garbage.

Ix.NET/Source/System.Interactive.Async/IAsyncEnumerable.cs

@@ -2,11 +2,6 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information. 
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-
 namespace System.Collections.Generic
 {
     /// <summary>
@@ -22,4 +17,4 @@ namespace System.Collections.Generic
         /// <returns>Enumerator for asynchronous enumeration over the sequence.</returns>
         IAsyncEnumerator<T> GetEnumerator();
     }
-}
+}

Ix.NET/Source/System.Interactive.Async/IAsyncEnumerator.cs

@@ -2,9 +2,6 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information. 
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -32,4 +29,4 @@ namespace System.Collections.Generic
         /// </returns>
         Task<bool> MoveNext(CancellationToken cancellationToken);
     }
-}
+}

Ix.NET/Source/System.Interactive.Async/IAsyncGrouping.cs

@@ -2,10 +2,7 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information. 
 
-using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
 
 namespace System.Linq
 {
@@ -13,4 +10,4 @@ namespace System.Linq
     {
         TKey Key { get; }
     }
-}
+}