Clean up `synchronize_chain_state_*` function confusion.

[afck]

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(From this comment.) We have:

• synchronize_chain_state(chain_id) which internally loads the committee and then synchronizes the state
• synchronize_chain_state_from_committee(committee) which requires committee but internally knows which chain to synchronize
• synchronize_chain_state_from_committee (on the client) that expects both

but we don't have fn synchronize_chain_state which hides both. Even though everything is available in the ChainClient:

• which chain it's for
• how to get the committee