Review the way we handle block rewards

[yarkinwho]

As touched in #80 , the current logic is we will return 0 if the consensus engine is not ethash.

However, though we are not using it in our node, the clique case needs to be considered. It is not ethash but it might have block rewards.

[stephenpdeos]

We want to change the logic to return 0 only when we are using our trust rule set

[yarkinwho]

More findings:
Upstream silkworm has inconsistency in the APIs regarding to this issue as well. So we should keep the current way for now and contact upstream first.

[yarkinwho]

Submitted erigontech/silkworm#1717