Fix project file

Ix.NET/Source/refs/System.Interactive/System.Interactive.csproj

@@ -13,8 +13,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\refs\System.Interactive\System.Interactive.csproj" ReferenceOutputAssembly="false" PrivateAssets="all" />
-
     <Compile Include="..\..\System.Interactive\**\*.cs" Exclude="..\..\System.Interactive\obj\**" />
   </ItemGroup>