Remove more F# duplicate package warnings

Author: Aaronontheweb

src/core/Akka.FSharp.Tests/Akka.FSharp.Tests.fsproj

@@ -26,7 +26,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="FSharp.Core" Version="$(FSharpVersion)" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />
     <PackageReference Include="xunit" Version="$(XunitVersion)" />
     <PackageReference Include="xunit.runner.visualstudio" Version="$(XunitVersion)" />