* BlockId removal: refactor: Backend::append_justification
It changes the arguments of `Backend::append_justification`
from: block: `BlockId<Block>` to: hash: `&Block::Hash`
This PR is part of `BlockId::Number` refactoring analysis (paritytech/substrate#11292)
* Error message improved
Co-authored-by: Adrian Catangiu <adrian@parity.io>
* single error message in beefy::finalize
* println removed
Co-authored-by: Adrian Catangiu <adrian@parity.io>