EmbedXaml: remove <None> items generated for XAML files by default

These items are generated by Microsoft.Net.SDK.DefaultItems.props, and
aren't supposed to be here.

build/EmbedXaml.props

@@ -4,6 +4,7 @@
      <Compile Update="**\*.xaml.cs">
       <DependentUpon>%(Filename)</DependentUpon>
     </Compile>
+    <None Remove="**\*.xaml"/>
     <AvaloniaResource Include="**\*.xaml">
       <SubType>Designer</SubType>
     </AvaloniaResource>