Re-enable Crossgen2 Json CG2 composite job once crossgen2 codegen failure is fixed

[LoopedBard3]

Tracking issue to re-enable the Crossgen2 Json CG2 composite job in benchmarks-ci-01 and benchmarks-ci-02 once the underlying crossgen2 issue is fixed.

It was disabled in #2177 because it was consistently failing during the crossgen2 composite publish step with:

error : Unhandled exception. ILCompiler.CodeGenerationFailedException: Code generation failed for method
        'Async variant: [Microsoft.AspNetCore.Components.Server]
         Microsoft.AspNetCore.Components.Server.Circuits.RemoteJSDataStream.CompletePipeAndDisposeStream(Exception)'
 ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
    at Internal.IL.Stubs.ILStubMethodIL.GetObject(...)
    at Internal.JitInterface.CorInfoImpl.HandleToModuleToken(...)
    at Internal.JitInterface.CorInfoImpl.ComputeMethodWithToken(...)
    at Internal.JitInterface.CorInfoImpl.getCallInfo(...)
    ...
error NETSDK1096: Optimizing assemblies for performance failed.

On Windows runs this additionally caused crank to hang, blocking the rest of the jobs in the pipeline.

To re-enable

Once the underlying crossgen2 codegen failure is resolved (and confirmed to no longer hang crank on Windows):

1. In build/crossgen2-scenarios.yml, change the CG2 composite profile's condition back from 'false' to 'true'.
2. Remove the explanatory comment block added above that profile in Disable Crossgen2 Json CG2 composite job #2177.
3. Verify a clean run of benchmarks-ci-01 and benchmarks-ci-02 with the profile re-enabled.

[DrewScoggins]

Also need to revert this. #2180