Simplify BlockOperation and remove unused members

[Geod24]

One of my current goals is to merge BlockOperation into BlockTransaction. This should make the code much simpler and the DB much less heavy. However, there's a few things that are currently blocking this:

• Usage of operation hashes
• The million way operations are indexed with something else
• The amount of duplication between operation and transaction

This addresses some of the 2nd and 3rd point. Operation hashes should be dealt with by using an unified way to access blocks/txs/ops (e.g. hash/hash/idx, hash/idx/idx or height/idx/idx).

[Geod24]

Updated according to @spikeekips 's comment