hygiene: Phase 3 — dead-code excision (~7,100 lines)

Third phase of the code-hygiene remediation: remove provably-dead code.
Each in-file deletion was adversarially verified (a per-finding investigator
plus a skeptic that greps the tree to refute deletability); the sanity grep
confirms zero dangling references, and the tree builds and self-mines clean.

Removed wholesale:
- src/cc/dapps/ (9 files, ~6,939 lines): a git-tracked but never-built Komodo
  DEX / z-migration tool (hushdex.c, zmigrate.c, cJSON.c, ...). Nothing in
  Makefile.am/configure.ac references it.

In-file dead code:
- pow.cpp: the `#ifdef original_algo` oldRT_CST_RST function (the macro is
  never defined in source or build flags) and two `if ( 0 )` debug blocks.
- walletdb.cpp: the "orphaned staking transaction" cleanup path (deadTxns) —
  DragonX is RandomX PoW with no staking, so the guard is always false and the
  block never runs; also drop the now-unused static/extern decls.
- cc/eval.h: the ProcessCC / Eval::ImportCoin / ImportPayout / DisputePayout
  declarations that have no definition anywhere in the tree.
- rpc/crosschain.cpp: the crosschainproof stub RPC (returned {} unconditionally)
  and its registrations in rpc/server.cpp, rpc/server.h, rpc/client.cpp.
- coins.cpp: the commented-out `//TODO: delete` Sprout PushAnchor template.
- wallet.cpp: the permanently-zero KMD `interest2` term in CreateTransaction.
- rpc/net.cpp: hush_longestchain's always-zero `n` var (num > (n>>1) => num>0)
  and its `if ( 0 )` debug branch.
- hush_nSPV.h / hush_nSPV_fullnode.h: three `if ( 0 && ... )` dead debug branches.
- net.cpp, crypter.h, saplingconsolidation.cpp (dup set_error_code),
  shieldcoinbase.cpp (`donation < 0` on a uint8_t), cclib.cpp (unused
  FAUCET2SIZE): single-line dead-code fixes.

Deliberately NOT touched (verification refuted the audit's "dead on DragonX"
premise): the ~2,250-line HUSH3 checkpoint block, the miner notary/timelock
paths, and hush_gateway.h — all reachable at runtime via -ac_name / -ac_*
args (the inherited Komodo assetchain model), and hush_gateway's
hush_opretvalidate is called from ConnectBlock (consensus). Dropping those
requires a deliberate decision to remove HAC/HUSH3 mode, tracked separately.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/wallet/walletdb.cpp

@@ -46,8 +46,6 @@ const int CHDChain::CURRENT_VERSION;
 using namespace std;
 
 static uint64_t nAccountingEntryNumber = 0;
-static list<uint256> deadTxns; 
-extern CBlockIndex *hush_blockindex(uint256 hash);
 
 //
 // CWalletDB
@@ -1017,8 +1015,7 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
                 {
                     // Leave other errors alone, if we try to fix them we might make things worse.
                     fNoncriticalErrors = true; // ... but do warn the user there is something wrong.
-                    // set rescan for any error that is not vin-empty on staking chains.
-                    if ( deadTxns.empty() && strType == "tx")
+                    if ( strType == "tx")
                         SoftSetBoolArg("-rescan", true);
                 }
             }
@@ -1034,29 +1031,6 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
         result = DB_CORRUPT;
     }
 
-    if ( !deadTxns.empty() )
-    {
-        // staking chains with vin-empty error is a failed staking tx. 
-        // we remove then re add the tx here to stop needing a full rescan, which does not actually fix the problem.
-        int32_t reAdded = 0;
-        BOOST_FOREACH (uint256& hash, deadTxns) 
-        {
-            fprintf(stderr, "Removing possible orphaned staking transaction from wallet.%s\n", hash.ToString().c_str());
-            if (!EraseTx(hash))
-                fprintf(stderr, "could not delete tx.%s\n",hash.ToString().c_str());
-            uint256 blockhash; CTransaction tx; CBlockIndex* pindex;
-            if ( GetTransaction(hash,tx,blockhash,false) && (pindex= hush_blockindex(blockhash)) != 0 && chainActive.Contains(pindex) )
-            {
-                CWalletTx wtx(pwallet,tx);
-                pwallet->AddToWallet(wtx, true, NULL);
-                reAdded++;
-            }
-        }
-        fprintf(stderr, "Cleared %li orphaned staking transactions from wallet. Readded %i real transactions.\n",deadTxns.size(),reAdded);
-        fNoncriticalErrors = false;
-        deadTxns.clear();
-    }
-    
     if (fNoncriticalErrors && result == DB_LOAD_OK)
         result = DB_NONCRITICAL_ERROR;