Remove unused var declarations.

Rx.NET/Source/src/System.Reactive/Linq/Observable/ConcatMany.cs

@@ -127,7 +127,7 @@ namespace System.Reactive.Linq.ObservableImpl
                 {
                     if (IsDisposed())
                     {
-                        while (_queue.TryDequeue(out var _))
+                        while (_queue.TryDequeue(out _))
                         {
                         }
                     }

Rx.NET/Source/src/System.Reactive/Linq/Observable/RetryWhen.cs

@@ -195,7 +195,7 @@ namespace System.Reactive.Linq.ObservableImpl
 
         private void Clear()
         {
-            while (_queue.TryDequeue(out var _))
+            while (_queue.TryDequeue(out _))
             {
                 ;
             }