scripted-diff: Replace ::mempool with m_node.mempool in tests

-BEGIN VERIFY SCRIPT-
 # tx pool member access (mempool followed by dot)
 sed --regexp-extended -i -e 's/(::)?\<mempool\>\.([a-zA-Z])/m_node.mempool->\2/g' $(git grep -l mempool ./src/test)
 # plain global (mempool not preceeded by dot, but followed by comma)
 sed --regexp-extended -i -e 's/([^\.])(::)?\<mempool\>,/\1*m_node.mempool,/g'     $(git grep -l mempool ./src/test)
-END VERIFY SCRIPT-

src/test/txvalidation_tests.cpp

@@ -34,17 +34,17 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_reject_coinbase, TestChain100Setup)
 
     LOCK(cs_main);
 
-    unsigned int initialPoolSize = mempool.size();
+    unsigned int initialPoolSize = m_node.mempool->size();
 
     BOOST_CHECK_EQUAL(
             false,
-            AcceptToMemoryPool(mempool, state, MakeTransactionRef(coinbaseTx),
+            AcceptToMemoryPool(*m_node.mempool, state, MakeTransactionRef(coinbaseTx),
                 nullptr /* plTxnReplaced */,
                 true /* bypass_limits */,
                 0 /* nAbsurdFee */));
 
     // Check that the transaction hasn't been added to mempool.
-    BOOST_CHECK_EQUAL(mempool.size(), initialPoolSize);
+    BOOST_CHECK_EQUAL(m_node.mempool->size(), initialPoolSize);
 
     // Check that the validation state reflects the unsuccessful attempt.
     BOOST_CHECK(state.IsInvalid());