Initial Crossgen2 fixes for composite R2R support (#31652)

Initial Crossgen2 fixes for composite R2R support (#31652)

With initial local changes to enable composite R2R I have finally
been able to compile a CoreCLR unit test in this mode. It doesn't
yet work at runtime, these changes just fix initial compiler issues
I hit during the build:

1) Delegate constructor signature was missing some comparison logic
that ended up asserting in the node comparer in the composite
build.

2) I have removed two seeminly superfluous parameters to
CreateMethodEntrypointNodeHelper.

3) I have removed an assertion related to multi-file RVA fields
that I believe to be no longer relevant after the refactorings
to copy the RVA fields around properly.

Thanks

Tomas