message: bench: Replace ::mempool globabl with test_setup.mempool
  This is a refactor, since they are aliases for each other
diff: @@ -44,7 +44,7 @@ static void AssembleBlock(benchmark::State& state)
  for (const auto& txr : txs) {
  TxValidationState state;
  - bool ret{::AcceptToMemoryPool(::mempool, state, txr, false /* plTxnReplaced */, false /* bypass_limits */)};
  + bool ret{::AcceptToMemoryPool(*test_setup.m_node.mempool, state, txr, false /* plTxnReplaced */, false /* bypass_limits */)};
  assert(ret);
  }
  }
  