remove obsolete comments

src/Avalonia.Themes.Default/TextBox.xaml

@@ -10,7 +10,6 @@
       <MenuItem x:Name="TextBoxContextFlyoutPasteItem" Header="Paste" Command="{Binding $parent[TextBox].Paste}" IsEnabled="{Binding $parent[TextBox].CanPaste}" InputGesture="{x:Static TextBox.PasteGesture}"/>
     </MenuFlyout>
 
-    <!-- ContextMenu obsolete, prefer ContextFlyout --> 
     <ContextMenu x:Key="DefaultTextBoxContextMenu" x:Name="TextBoxContextMenu">
       <MenuItem x:Name="TextBoxContextMenuCutItem" Header="Cut" Command="{Binding $parent[TextBox].Cut}" IsEnabled="{Binding $parent[TextBox].CanCut}" InputGesture="{x:Static TextBox.CutGesture}" />
       <MenuItem x:Name="TextBoxContextMenuCopyItem" Header="Copy" Command="{Binding $parent[TextBox].Copy}" IsEnabled="{Binding $parent[TextBox].CanCopy}" InputGesture="{x:Static TextBox.CopyGesture}"/>

src/Avalonia.Themes.Fluent/Controls/TextBox.xaml

@@ -21,7 +21,6 @@
       <MenuItem x:Name="TextBoxContextFlyoutPasteItem" Header="Paste" Command="{Binding $parent[TextBox].Paste}" IsEnabled="{Binding $parent[TextBox].CanPaste}" InputGesture="{x:Static TextBox.PasteGesture}"/>
     </MenuFlyout>
 
-    <!-- ContextMenu obsolete, prefer ContextFlyout -->
     <ContextMenu x:Key="DefaultTextBoxContextMenu" x:Name="TextBoxContextMenu">
       <MenuItem x:Name="TextBoxContextMenuCutItem" Header="Cut" Command="{Binding $parent[TextBox].Cut}" IsEnabled="{Binding $parent[TextBox].CanCut}" InputGesture="{x:Static TextBox.CutGesture}" />
       <MenuItem x:Name="TextBoxContextMenuCopyItem" Header="Copy" Command="{Binding $parent[TextBox].Copy}" IsEnabled="{Binding $parent[TextBox].CanCopy}" InputGesture="{x:Static TextBox.CopyGesture}"/>