Removed using directives which no longer exist

Author: jamesmcroft

Microsoft.Toolkit.Uwp.UI.Controls.Layout/Carousel/Carousel.cs

@@ -6,7 +6,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.Toolkit.Uwp.UI.Automation.Peers;
-using Microsoft.Toolkit.Uwp.UI.Extensions;
 using Windows.Foundation;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Automation;

Microsoft.Toolkit.Uwp.UI.Controls.Layout/Carousel/CarouselItemAutomationPeer.cs

@@ -3,7 +3,6 @@
 // See the LICENSE file in the project root for more information.
 
 using Microsoft.Toolkit.Uwp.UI.Controls;
-using Microsoft.Toolkit.Uwp.UI.Extensions;
 using Windows.UI.Xaml.Automation;
 using Windows.UI.Xaml.Automation.Peers;
 using Windows.UI.Xaml.Automation.Provider;

UnitTests/UnitTests.UWP/UI/Controls/Test_Carousel.cs

@@ -8,8 +8,8 @@
 using Windows.UI.Xaml.Automation;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Windows.UI.Xaml.Automation.Peers;
+using Microsoft.Toolkit.Uwp;
 using Microsoft.Toolkit.Uwp.UI.Automation.Peers;
-using Microsoft.Toolkit.Uwp.Extensions;
 using Microsoft.Toolkit.Uwp.UI.Controls;
 
 namespace UnitTests.UWP.UI.Controls