* BlockId removal: refactor: BlockBackend::block|block_status

It changes the arguments of:
-  `BlockBackend::block`
-  `BlockBackend::block_status`

method from: `BlockId<Block>` to: `Block::Hash`

This PR is part of BlockId::Number refactoring analysis (paritytech/substrate#11292)

* non-obvious reworks

* doc fix

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: parity-processbot <>