Undo SDK workaround for props import issue after updating to Preview 4 SDK

[ryalanms]

Remove WPF's workaround for SDK issue: dotnet/sdk#16725.

https://github.com/dotnet/wpf/blob/main/eng/WpfArcadeSdk/tools/Wpf.Cpp.props#L12

    <!-- This should be removed when .NET 6 Preview 4 becomes available. P4 contains the SDK fix. --> 
    <!--    https://github.com/dotnet/core/issues/6066 -->
    <!--    https://github.com/dotnet/sdk/issues/16725 -->
    <ILLinkTasksAssembly>DummyPropertyValueForILLinkTasksAssembly</ILLinkTasksAssembly>