Revert "Update test projects to use latest Roslyn."

This reverts commit dotnet/aspnetcore-tooling@cff58c01ae.
\n\nCommit migrated from 7388cde7ea

src/Razor/Microsoft.NET.Sdk.Razor/test/IntegrationTests/BuildServerIntegrationTest.cs

@@ -77,12 +77,6 @@ namespace Microsoft.AspNetCore.Razor.Design.IntegrationTests
         [InitializeTestProject(originalProjectName: "SimpleMvc", targetProjectName: "Whitespace in name", baseDirectory: "")]
         public async Task Build_AppWithWhitespaceInName_CanBuildSuccessfully()
         {
-            // We need to separately restore the project in order to ensure this project uses the latest Roslyn. Without this
-            // the Csc task from Roslyn would have already been loaded and any update to it from nuget packages would not have
-            // an effect. This allows us to create our obj/Whitespace in name.csproj.nuget.g.props file (we renamed the project)
-            // and then properly build the project with an appropriate Csc.
-            await DotnetMSBuild("Restore");
-
             var result = await DotnetMSBuild(
                 "Build",
                 "/p:_RazorForceBuildServer=true");

src/Razor/test/testassets/Directory.Build.props

@@ -38,26 +38,4 @@
 
   <Import Project="After.Directory.Build.props" Condition="Exists('After.Directory.Build.props')" />
 
-  <!--
-    NOTE, BELOW
-
-    These bits are a temporary workaround until we're able to get on the latest SDK which includes the latest Roslyn bits.
-    Without them we can't properly publish testapps in a standalone fashion without investing in temporary infrastructure.
-  -->
-  <PropertyGroup>
-    <MicrosoftNetCompilersToolsetPackageVersion>3.3.0-beta2-19365-06</MicrosoftNetCompilersToolsetPackageVersion>
-    <RestoreSources Condition="'$(DotNetBuildOffline)' != 'true' ">
-      $(RestoreSources);
-      https://dotnet.myget.org/F/roslyn/api/v3/index.json;
-    </RestoreSources>
-  </PropertyGroup>
-  
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Net.Compilers.Toolset"
-        Version="$(MicrosoftNetCompilersToolsetPackageVersion)"
-        PrivateAssets="all"
-        IsImplicitlyDefined="true" />
-  </ItemGroup>
-
-
 </Project>