System.Runtime no longer needs to enable preview features

Author: jeffhandley

src/libraries/System.Runtime/src/System.Runtime.csproj

@@ -3,9 +3,6 @@
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <Nullable>enable</Nullable>
-    <!-- The following 2 lines disable the automatic generation of the [RequiresPreviewFeatures] assembly level attribute and set LangVersion to Preview on the latest TFM-->
-    <EnablePreviewFeatures>True</EnablePreviewFeatures>
-    <GenerateRequiresPreviewFeaturesAttribute>False</GenerateRequiresPreviewFeaturesAttribute>
   </PropertyGroup>
   <ItemGroup>
     <!-- Compiler throws error if you try to use System.Void and instructs you to use void keyword instead. So we have manually added a typeforward for this type. -->