Call TransactionRemovedFromMempool in the CScheduler thread

This is both good practice (we want to move all such callbacks
into a background thread eventually) and prevents a lock inversion
when we go to use this in wallet (mempool.cs->cs_wallet and
cs_wallet->mempool.cs would otherwise both be used).

src/validationinterface.cpp

@@ -106,7 +106,9 @@ void UnregisterAllValidationInterfaces() {
 
 void CMainSignals::MempoolEntryRemoved(CTransactionRef ptx, MemPoolRemovalReason reason) {
     if (reason != MemPoolRemovalReason::BLOCK && reason != MemPoolRemovalReason::CONFLICT) {
-        m_internals->TransactionRemovedFromMempool(ptx);
+        m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] {
+            m_internals->TransactionRemovedFromMempool(ptx);
+        });
     }
 }