Use mempool/txgraph to determine if a tx has descendants

Remove a reference to GetCountWithDescendants() in preparation for removing
this function and the associated cached state from the mempool.

src/node/interfaces.cpp

@@ -665,10 +665,7 @@ public:
     bool hasDescendantsInMempool(const Txid& txid) override
     {
         if (!m_node.mempool) return false;
-        LOCK(m_node.mempool->cs);
+        return m_node.mempool->HasDescendants(txid);
-        const auto entry{m_node.mempool->GetEntry(txid)};
-        if (entry == nullptr) return false;
-        return entry->GetCountWithDescendants() > 1;
     }
     bool broadcastTransaction(const CTransactionRef& tx,
         const CAmount& max_tx_fee,

src/txmempool.cpp

@@ -229,6 +229,14 @@ util::Result<void> CTxMemPool::CheckPackageLimits(const Package& package,
     return {};
 }
 
+bool CTxMemPool::HasDescendants(const Txid& txid) const
+{
+    LOCK(cs);
+    auto entry = GetEntry(txid);
+    if (!entry) return false;
+    return m_txgraph->GetDescendants(*entry, TxGraph::Level::MAIN).size() > 1;
+}
+
 util::Result<CTxMemPool::setEntries> CTxMemPool::CalculateMemPoolAncestors(
     const CTxMemPoolEntry &entry,
     const Limits& limits,

src/txmempool.h

@@ -467,6 +467,8 @@ public:
         const Limits& limits,
         bool fSearchForParents = true) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
+    bool HasDescendants(const Txid& txid) const;
+
     /** Collect the entire cluster of connected transactions for each transaction in txids.
      * All txids must correspond to transaction entries in the mempool, otherwise this returns an
      * empty vector. This call will also exit early and return an empty vector if it collects 500 or