The 3 proofs can be reworked to two proofs as we can use the
BeaconBlock directly instead of BeaconBlockHeader and
BeaconBlockBody. This is possible because the HTR of the
BeaconBlock is the same as the one of the BeaconBlockHeader.
This results in 32 bytes less as an intermediate hash can be
removed. But more importantly looks more clean and compact in
structure and code.