Remove Merge by TTD functionality

[garyschulte]

Remove Merge transition by TTD. Removing the merge will clean up a lot of dead code, and simplify the full sync strategy and the blockchain portion of snap sync pipeline. Unblocks dropping chain history in proto-EIP-4444 scope agreed upon at devcon SEA

Besu still treats the merge explicitly in some cases. Notably the full sync strategy will "forward sync" up until the merge at TTD, then "backward sync" from the head of the chain back to the merge. The blockchain portion of the snap sync pipeline has the same pre/post merge logic, which is just tech debt by now.

Acceptance Criteria

• remove merge specific classes, "Transition*" classes which wrap pre and post merge objects
• simplify full sync strategy to not rely on "backward sync" code for all blocks since merge
• remove merge-specific triggers and listeners in favor of explicit merge block definitions for the affected networks, for things like protocol schedule changes, chain head rules, etc.

[garyschulte]

this branch is a first pass at this PR:https://github.com/garyschulte/besu/tree/feature/remove-merge