fuzz: Avoid timeout in utxo_total_supply #27780

Looks like for high block counts it may be better to mock the chain, otherwise a high limit will lead to fuzz input bloat and timeouts, see #17860 (comment).

It can be checked that the fuzz target can still find the CVE, see #17860#pullrequestreview-1410594057 with a diff of:

diff --git a/src/consensus/tx_check.cpp b/src/consensus/tx_check.cpp
index f949655909..6f4cfb5f51 100644
--- a/src/consensus/tx_check.cpp
+++ b/src/consensus/tx_check.cpp
@@ -39,8 +39,6 @@ bool CheckTransaction(const CTransaction& tx, TxValidationState& state)
     // the underlying coins database.
     std::set<COutPoint> vInOutPoints;
     for (const auto& txin : tx.vin) {
-        if (!vInOutPoints.insert(txin.prevout).second)
-            return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-inputs-duplicate");
     }
 
     if (tx.IsCoinBase())

Also, fix a nit, see #17860 (review)

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--021abf342d371248e50ceaed478a90ca-->

Reviews

See the guideline for information on the review process.

If your review is incorrectly listed, please react with 👎 to this comment and the bot will ignore it on the next update.

ACK fafb4da121b19ba1b7bd173e25651c64d1982fb4

Verified that the target still finds the CVE with the patch applied.