Removed AvaloniaDisposable.

No longer used.

src/Avalonia.Base/AvaloniaDisposable.cs

@@ -1,41 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using Avalonia.Platform;
-
-namespace Avalonia
-{
-    public abstract class AvaloniaDisposable : IDisposable
-    {
-#if DEBUG_DISPOSE
-        public string DisposedAt { get; private set; }
-#endif
-
-
-        public bool IsDisposed { get; private set; }
-
-        public void Dispose()
-        {
-            IsDisposed = true;
-#if DEBUG_DISPOSE
-            DisposedAt = AvaloniaLocator.Current.GetService<IRuntimePlatform>().GetStackTrace();
-#endif
-            DoDispose();
-        }
-
-        protected void CheckDisposed()
-        {
-            if (IsDisposed)
-                throw new ObjectDisposedException(GetType().FullName
-#if DEBUG_DISPOSE
-                    , "Disposed at: \n" + DisposedAt
-#endif
-
-                    );
-        }
-
-        protected abstract void DoDispose();
-    }
-}