wallet: Remove chainStateFlushed

chainStateFlushed is no longer needed since the best block is updated
after a block is scanned. Since the chainstate being flushed does not
necessarily coincide with the wallet having processed said block, it
does not entirely make sense for the wallet to be recording that block
as its best block, and this can cause race conditions where some blocks
are not processed. Thus, remove this notification.

src/bench/wallet_migration.cpp

@@ -28,7 +28,6 @@ static void WalletMigration(benchmark::Bench& bench)
 
     // Setup legacy wallet
     std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(test_setup->m_node.chain.get(), "", CreateMockableWalletDatabase());
-    wallet->chainStateFlushed(ChainstateRole::NORMAL, CBlockLocator{});
     LegacyDataSPKM* legacy_spkm = wallet->GetOrCreateLegacyDataSPKM();
     WalletBatch batch{wallet->GetDatabase()};