Re-enable framework tests (#13043)

Author: John Luo

src/Framework/test/Microsoft.AspNetCore.App.UnitTests.csproj

@@ -5,8 +5,6 @@
     <RootNamespace>Microsoft.AspNetCore</RootNamespace>
     <!-- https://github.com/aspnet/AspNetCore/issues/7939: This unit test requires the shared framework be available in Helix. -->
     <BuildHelixPayload>false</BuildHelixPayload>
-    <!-- Test logic needs to be updated to handle when SharedFx version and TFM are not the same -->
-    <SkipTests>true</SkipTests>
   </PropertyGroup>
 
   <ItemGroup>