Remove unneeded file copying

Now that the netstandard2.0 references are available via the
MS.CA.Test.Reosurces.Proprietary NuGet package we no longer need to copy
them around on the file system (that's where they were previously being
referenced from).

build/Targets/Roslyn.Toolsets.Xunit.targets

@@ -20,26 +20,6 @@
   </PropertyGroup>
     
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp2.0'">
-    <Content Include="$(NetStandard20RefPath)\netstandard.dll">
-      <Link>ref/%(FileName)%(Extension)</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <Visible>false</Visible>
-    </Content>
-    <Content Include="$(NetStandard20RefPath)\mscorlib.dll">
-      <Link>ref/%(FileName)%(Extension)</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <Visible>false</Visible>
-    </Content>
-    <Content Include="$(NetStandard20RefPath)\System.Runtime.dll">
-      <Link>ref/%(FileName)%(Extension)</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <Visible>false</Visible>
-    </Content>
-    <Content Include="$(NetStandard20RefPath)\System.Dynamic.Runtime.dll">
-      <Link>ref/%(FileName)%(Extension)</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <Visible>false</Visible>
-    </Content>
     <Content Include="$(MicrosoftCSharpRefPath)\Microsoft.CSharp.dll">
       <Link>ref/%(FileName)%(Extension)</Link>
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>

build/Targets/Settings.props

@@ -58,7 +58,6 @@
     <IntermediateOutputPath>$(BaseIntermediateOutputPath)$(Configuration)</IntermediateOutputPath>
     <ArtifactsSymStoreDirectory Condition="'$(DeveloperBuild)' != 'true' and '$(OS)' == 'Windows_NT'">$(BaseOutputPath)$(Configuration)\SymStore\</ArtifactsSymStoreDirectory>
 
-    <NetStandard20RefPath>$(NuGetPackageRoot)/netstandard.library/$(NETStandardLibraryFixedVersion)/build/netstandard2.0/ref/</NetStandard20RefPath>
     <MicrosoftCSharpRefPath>$(NuGetPackageRoot)/microsoft.csharp/$(MicrosoftCSharpVersion)/ref/netstandard1.0/</MicrosoftCSharpRefPath>
 
     <ToolsetPackagesSemaphore>$(ToolsetPackagesDir)toolsetpackages.semaphore</ToolsetPackagesSemaphore>