Remove the Windows.Desktop.App framework dependency in System.Reactive

Rx.NET/Source/facades/System.Reactive/System.Reactive.nuspec

@@ -51,9 +51,7 @@
     </dependencies>
     <frameworkReferences>
       <group targetFramework="net8.0" />
-      <group targetFramework="net8.0-windows10.0.19041">
-        <frameworkReference name="Microsoft.WindowsDesktop.App" />
-      </group>
+      <group targetFramework="net8.0-windows10.0.19041" />
       <group targetFramework=".NETFramework4.7.2" />
       <group targetFramework=".NETStandard2.0" />
       <group targetFramework="UAP10.0.18362" />