Refactor get_attesting_indices

[mehdi-aouadi]

Refactor get_attesting_indices

def get_attesting_indices(state: BeaconState,
                          data: AttestationData,
                          bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> Set[ValidatorIndex]:
    """
    Return the set of attesting indices corresponding to ``data`` and ``bits``.
    """
    committee = get_beacon_committee(state, data.slot, data.index)
    return set(index for i, index in enumerate(committee) if bits[i])

Becomes

def get_attesting_indices(state: BeaconState, attestation: Attestation) -> Set[ValidatorIndex]:
    """
    Return the set of attesting indices corresponding to ``data`` and ``bits``.
    """
    committee = get_beacon_committee(state, attestation.data.slot, attestation.data.index)
    return set(index for i, index in enumerate(committee) if attestation.aggregation_bits[i])

Link to the spec change