Delete FEATURE_READYTORUN_COMPILER ifdef

[MichalStrehovsky]

#103361 resurrected this long-deleted ifdef (it's crossgen1-specific define).

I actually wonder if we should roll back all changes to getHeapClassSize - @EgorBo's #104411 doesn't fix getHeapClassSize to work with valuetypes and we don't have any failing tests, so maybe it doesn't need to handle valuetypes?

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[AndyAyersMS]

I actually wonder if we should roll back all changes to getHeapClassSize - @EgorBo's #104411 doesn't fix getHeapClassSize to work with valuetypes and we don't have any failing tests, so maybe it doesn't need to handle valuetypes?

I think we could, yes, since we're mapping boxed value types to the internal box ref class.

[MichalStrehovsky]

I think we could, yes, since we're mapping boxed value types to the internal box ref class.

I've done that so that we don't need to synchronize this to the managed impl.