scripted-diff: test: Use CTxMemPool in TestingSetup

After this commit, there should be no explicit instantiation of
CTxMemPool in src/test other than those in fuzz/ and setup_common

-BEGIN VERIFY SCRIPT-
find_regex="CTxMemPool\s+([^;({]+)(|\(\)|\{\});" \
    && git grep -l -E "$find_regex" -- src/test \
        | grep -v -e "^src/test/util/setup_common.cpp$" \
                  -e "^src/test/fuzz/" \
        | xargs sed -i -E "s@$find_regex@CTxMemPool\& \1 = *Assert(m_node.mempool);@g"
-END VERIFY SCRIPT-

src/test/validation_chainstate_tests.cpp

@@ -30,7 +30,7 @@ BOOST_AUTO_TEST_CASE(validation_chainstate_resize_caches)
     ChainstateManager manager{chainman_opts};
 
     WITH_LOCK(::cs_main, manager.m_blockman.m_block_tree_db = std::make_unique<CBlockTreeDB>(1 << 20, true));
-    CTxMemPool mempool;
+    CTxMemPool& mempool = *Assert(m_node.mempool);
 
     //! Create and add a Coin with DynamicMemoryUsage of 80 bytes to the given view.
     auto add_coin = [](CCoinsViewCache& coins_view) -> COutPoint {