cleanup too

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

@@ -373,7 +373,6 @@ namespace System.Linq.Internal
             return Task.FromResult(array);
         }
 
-
         public Task<List<IGrouping<TKey, TElement>>> ToListAsync(CancellationToken cancellationToken)
         {
             var list = new List<IGrouping<TKey, TElement>>(Count);

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

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -52,6 +53,8 @@ namespace System.Linq
 
             public OnErrorResumeNextAsyncIterator(IEnumerable<IAsyncEnumerable<TSource>> sources)
             {
+                Debug.Assert(sources != null);
+
                 this.sources = sources;
             }
 

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

@@ -2,11 +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;
-using System.Threading.Tasks;
 
 namespace System.Linq
 {