cleaned-up dispose TODO (#22703)

src/modules/previewpane/common/examplehandler/TestCustomHandler.cs

@@ -45,8 +45,6 @@ namespace Common
                     _previewHandlerControl.Dispose();
                 }
 
-                // TODO: free unmanaged resources (unmanaged objects) and override finalizer
-                // TODO: set large fields to null
                 disposedValue = true;
             }
         }