Code Quality: Removed unused reference to WinUIEx

Author: yaira2

src/Files.App/UserControls/FilePreviews/MediaPreview.xaml

@@ -6,7 +6,6 @@
 	xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
 	xmlns:local="using:Files.App.UserControls.FilePreviews"
 	xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-	xmlns:winex="using:WinUIEx"
 	d:DesignHeight="300"
 	d:DesignWidth="400"
 	Unloaded="{x:Bind ViewModel.PreviewControlBase_Unloaded}"