Disable implicit F# core reference

Avoids NU1504 Duplicate 'PackageReference' items found

vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj

@@ -30,6 +30,7 @@
     <EnablePackageSigning>false</EnablePackageSigning>
     <UseSGen>false</UseSGen>
     <IncludeMonoRuntime>false</IncludeMonoRuntime>
+    <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DefineConstants>;RELEASE</DefineConstants>