See design-doc: https://github.com/ethereum-optimism/design-docs/blob/main/protocol/deprecate-reqresp-sync.md

This aims to fix sync problems seen with the old req-resp protocol based syncing.

The related op-node CLI flags need deprecation, and sync behavior needs to change as described in the design-doc.
The CLI sync-flag should be a no-op.

An explicit --skip-initial-l1-sync should be introduced for users who aim to verify the chain starting after an initial EL sync.