refactor(iota-core): Remove incorrect AuthorityState ::state comment

[bingyanglin]

Description of change

Remove the incorrect comment.

The TODO comment to remove the AuthorityState ::state was written in this Sui commit d6a9015 at Jan 27, 2024.
However, the AuthorityState ::state is then used in object_cache_reader and transaction_cache_reader in the later Sui Commit 6243a15 at May 17, 2024. In addition, the transaction_manager which is cloned from AuthorityState ::state is also used to call the enqueue_with_expected_effects_digest method.

Thus the AuthorityState::state should not be removed, and the incorrect TODO comment should be removed.

Links to any relevant issues

Part of #2092

Type of change

• Enhancement

How the change has been tested

Ran the local network with RUST_LOG=info cargo run --release --bin iota start --force-regenesis --with-faucet

Change checklist

Tick the boxes that are relevant to your changes, and delete any items that are not.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes