Remove nuget package System.ValueTuple in Test project

Author: bjornhellander

StyleCop.Analyzers/StyleCop.Analyzers.Test/StyleCop.Analyzers.Test.csproj

@@ -16,7 +16,6 @@
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="1.3.2" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.XUnit" Version="1.1.2-beta1.23509.1" />
     <PackageReference Include="Microsoft.VisualStudio.Composition" Version="16.1.8" />
-    <PackageReference Include="System.ValueTuple" Version="4.5.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="Xunit.Combinatorial" Version="1.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" PrivateAssets="all" />