The latest version of ilasm produced by coreclr is now a fully
independent executable; it no longer depends on having a full runtime
laid down next to it.

This means we can vastly simplify how it is deployde in our
infrastructure. The package can now be included and have ilasm manually
copied out. This is similar to the approach that we take for our
diasymreader native dependencies.

closes #37582
related #25930, #25144