Update Calendar.xml

src/XamlPlayground/Samples/Calendar.xml

@@ -1,6 +1,5 @@
 <UserControl xmlns="https://github.com/avaloniaui"
-             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             x:Class="ControlCatalog.Pages.CalendarPage">
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
   <StackPanel Orientation="Vertical" Spacing="4">
     <TextBlock Classes="h2">A calendar control for selecting dates</TextBlock>