Update samples/Sandbox/MainWindow.axaml

Co-authored-by: Max Katz <maxkatz6@outlook.com>

samples/Sandbox/MainWindow.axaml

@@ -1,19 +1,4 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
         x:Class="Sandbox.MainWindow">
-  <Border Background="LightGray" HorizontalAlignment="Center" VerticalAlignment="Center">
-    <StackPanel>
-      <RichTextBlock x:Name="txtBlock" IsTextSelectionEnabled="True" Margin="10" TextWrapping="Wrap">
-        This <Span FontWeight="Bold">is</Span> a
-        <Span Background="Silver" Foreground="Maroon">TextBlock</Span>
-        with <Span TextDecorations="Underline">several</Span>
-        <Span FontStyle="Italic">Span</Span> elements,
-        <Span Foreground="Blue">
-          using a <Bold>variety</Bold> of <Italic>styles</Italic>
-        </Span>.
-      </RichTextBlock>
-      <TextBox Text="{Binding #txtBlock.SelectedText}"/>
-      <TextBlock Text="{Binding #txtBlock.Text}"/>
-    </StackPanel>
-  </Border>
 </Window>