Merge #20588: Remove unused and confusing CTransaction constructor

fac39c1983 wallet: document that tx in CreateTransaction is purely an out-param (MarcoFalke)
faac31521b Remove unused and confusing CTransaction constructor (MarcoFalke)

Pull request description:

  The constructor is confusing and dangerous (as explained in the TODO), fix that by removing it.

ACKs for top commit:
  laanwj:
    Code review ACK fac39c1983
  promag:
    Code review ACK fac39c1983.
  theStack:
    Code review ACK fac39c1983

Tree-SHA512: e0c8cffce8d8ee0166b8e1cbfe85ed0657611e26e2af0d69fde70eceaa5d75cbde3eb489af0428fe4fc431360b4c791fb1cc21b8dee7d4c7a4f17df00836229d

src/test/fuzz/script_sigcache.cpp

@@ -29,7 +29,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
 
     const std::optional<CMutableTransaction> mutable_transaction = ConsumeDeserializable<CMutableTransaction>(fuzzed_data_provider);
-    const CTransaction tx = mutable_transaction ? CTransaction{*mutable_transaction} : CTransaction{};
+    const CTransaction tx{mutable_transaction ? *mutable_transaction : CMutableTransaction{}};
     const unsigned int n_in = fuzzed_data_provider.ConsumeIntegral<unsigned int>();
     const CAmount amount = ConsumeMoney(fuzzed_data_provider);
     const bool store = fuzzed_data_provider.ConsumeBool();

src/test/fuzz/transaction.cpp

@@ -42,7 +42,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
             return CTransaction(deserialize, ds);
         } catch (const std::ios_base::failure&) {
             valid_tx = false;
-            return CTransaction();
+            return CTransaction{CMutableTransaction{}};
         }
     }();
     bool valid_mutable_tx = true;