feat: remove achieved difficulty calculation and submit block to base node

[hansieodendaal]

Description

Removed achieved difficulty calculation and submit block to base node, as this will be done by the respective miners/merge mining proxy.

Motivation and Context

It is not efficient for the sha-p2pool to recalculate difficulty nor to submit the mined block with appropriate achieved difficulty to the base node, as the miners already calculate the achieved difficulty and can submit the block directly to the base node instead of via a 3rd party (the sha-p2pool in this case).

How Has This Been Tested?

Waiting for system-level testing.

What process can a PR reviewer use to test or verify this change?

Code review.

Breaking Changes

• None
• Requires data directory on base node to be deleted
• Requires hard fork
• Other - Please specify

BREAKING CHANGE:

• Miners must submit blocks with appropriate achieved difficulty to the base node directly before submitting it to the sha-p2pool.
• gRPC GetNewBlockResponse interface change.