Remove receive_certificate_and_update_validators; fix flaky test. (#4805)

## Motivation

`test_memory_cross_chain_message` is flaky;
`receive_certificate_and_update_validators` sometimes fails. But this
method is not expected to work anymore since sender chains are now
sparse and it tries to get the local chain info for the sender chain.
Also, it is used only in tests.

## Proposal

Remove it. Use `synchronize_from_validators` or
`synchronize_chain_state` instead.

## Test Plan

CI

## Release Plan

- These changes should be backported to `testnet_conway`.

## Links

- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

Author: afck

linera-core/benches/client_benchmarks.rs

@@ -54,39 +54,30 @@ pub async fn run_claim_bench<B>(
     let amt = Amount::ONE;
 
     let account = Account::new(chain2.chain_id(), owner1);
-    let cert = chain1
+    chain1
         .transfer_to_account(AccountOwner::CHAIN, amt, account)
         .await
         .unwrap()
         .unwrap();
 
-    chain2
-        .receive_certificate_and_update_validators(cert)
-        .await
-        .unwrap();
+    chain2.synchronize_from_validators().await.unwrap();
     chain2.process_inbox().await.unwrap();
     assert_eq!(
         chain1.local_balance().await.unwrap(),
         Amount::from_tokens(9)
     );
 
     let account = Account::chain(chain1.chain_id());
-    let cert = chain1
+    chain1
         .claim(owner1, chain2.chain_id(), account, amt)
         .await
         .unwrap()
         .unwrap();
 
-    chain2
-        .receive_certificate_and_update_validators(cert)
-        .await
-        .unwrap();
-    let cert = chain2.process_inbox().await.unwrap().0.pop().unwrap();
+    chain2.synchronize_from_validators().await.unwrap();
+    chain2.process_inbox().await.unwrap().0.pop().unwrap();
 
-    chain1
-        .receive_certificate_and_update_validators(cert)
-        .await
-        .unwrap();
+    chain1.synchronize_from_validators().await.unwrap();
     chain1.process_inbox().await.unwrap();
     assert_eq!(
         chain1.local_balance().await.unwrap(),

linera-core/src/client/mod.rs

@@ -621,7 +621,7 @@ impl<Env: Environment> Client<Env> {
         let certificate = self
             .communicate_chain_action(committee, finalize_action, hashed_value)
             .await?;
-        self.receive_certificate(certificate.clone(), ReceiveCertificateMode::AlreadyChecked)
+        self.receive_certificate_with_checked_signatures(certificate.clone())
             .await?;
         Ok(certificate)
     }
@@ -735,51 +735,16 @@ impl<Env: Environment> Client<Env> {
         Ok(certificate)
     }
 
-    /// Processes the confirmed block certificate and its ancestors in the local node, then
-    /// updates the validators up to that certificate.
+    /// Processes the confirmed block certificate in the local node without checking signatures.
+    /// Also downloads and processes all ancestors that are still missing.
     #[instrument(level = "trace", skip_all)]
-    async fn receive_certificate_and_update_validators(
+    async fn receive_certificate_with_checked_signatures(
         &self,
         certificate: ConfirmedBlockCertificate,
-        mode: ReceiveCertificateMode,
-    ) -> Result<(), ChainClientError> {
-        let block_chain_id = certificate.block().header.chain_id;
-        let block_height = certificate.block().header.height;
-
-        self.receive_certificate(certificate, mode).await?;
-
-        // Make sure a quorum of validators (according to the chain's new committee) are up-to-date
-        // for data availability.
-        let local_committee = self
-            .chain_info_with_committees(block_chain_id)
-            .await?
-            .into_current_committee()?;
-        self.communicate_chain_updates(
-            &local_committee,
-            block_chain_id,
-            block_height.try_add_one()?,
-            CrossChainMessageDelivery::Blocking,
-        )
-        .await?;
-        Ok(())
-    }
-
-    /// Processes the confirmed block certificate in the local node. Also downloads and processes
-    /// all ancestors that are still missing.
-    #[instrument(level = "trace", skip_all)]
-    async fn receive_certificate(
-        &self,
-        certificate: ConfirmedBlockCertificate,
-        mode: ReceiveCertificateMode,
     ) -> Result<(), ChainClientError> {
         let certificate = Box::new(certificate);
         let block = certificate.block();
 
-        // Verify the certificate before doing any expensive networking.
-        let (max_epoch, committees) = self.admin_committees().await?;
-        if let ReceiveCertificateMode::NeedsCheck = mode {
-            Self::check_certificate(max_epoch, &committees, &certificate)?.into_result()?;
-        }
         // Recover history from the network.
         self.download_certificates(block.header.chain_id, block.header.height)
             .await?;
@@ -3405,24 +3370,6 @@ impl<Env: Environment> ChainClient<Env> {
         self.update_state(|state| state.clear_pending_proposal());
     }
 
-    /// Processes a confirmed block for which this chain is a recipient and updates validators.
-    #[instrument(
-        level = "trace",
-        skip(certificate),
-        fields(certificate_hash = ?certificate.hash()),
-    )]
-    pub async fn receive_certificate_and_update_validators(
-        &self,
-        certificate: ConfirmedBlockCertificate,
-    ) -> Result<(), ChainClientError> {
-        self.client
-            .receive_certificate_and_update_validators(
-                certificate,
-                ReceiveCertificateMode::NeedsCheck,
-            )
-            .await
-    }
-
     /// Rotates the key of the chain.
     ///
     /// Replaces current owners of the chain with the new key pair.