Fix codegen validation when Runtime APIs are stripped

[jsdw]

The CLI tool can now strip out specific runtime APIs as well as specific pallets.

We have a method in the codegen called validate_codegen which compares some node metadata against the generated code. It takes into account only those pallets that we explicitly generated, but does not do the same for Runtime APIs (so when runtime APIs are stripped the metadata will never compare equal to node metadata).

Let's fix that (preferably after #974 merges since it changes things in this area).