Test generator blocking issue

There appears to be some issue in the generator.

This is probably the real reason the test in the following issue stalled:

* #4705

For some reason, these two tests were added to `active_tests` but never printed "Starting" and never actually executed.

It's as if line 181 were forever blocked & therefore in deadlock.

https://github.com/ethereum/consensus-specs/blob/92dda6fbb137a44fb443630c65b0f421c921d0cb/tests/core/pyspec/eth2spec/gen_helpers/gen_base/gen_runner.py#L181-L183

I'm really not sure what's going on here. Probably time to just retire the custom test generator & do pytest.

* #4709