- remove unused using

Lib.Audio/Channel.cs

@@ -2,7 +2,6 @@
 // Created: 2021-04-07
 // Copyright(c) 2021 SimonG. All Rights Reserved.
 
-using System;
 using System.Collections.Generic;
 using Lib.Audio.Controls.Buttons.Factories;
 using Lib.Audio.Controls.Buttons.Interfaces;