Remove un-needed usings

Author: Rosuavio

Microsoft.Toolkit.Uwp.UI.Controls.Input/RangeSelector/RangeSelector.Input.Pointer.cs

@@ -3,13 +3,9 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
-using Windows.Foundation;
-using Windows.System;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
-using Windows.UI.Xaml.Controls.Primitives;
 using Windows.UI.Xaml.Input;
-using Windows.UI.Xaml.Shapes;
 
 namespace Microsoft.Toolkit.Uwp.UI.Controls
 {