Merge bitcoin/bitcoin#35914: test, fuzz: Remove unused variables

3175d57628 test, refactor: Remove unused `error` in `wallet_tests.cpp` (Hennadii Stepanov)
422f1bd92f test, refactor: Remove unused `utxo_pool` in `coinselector_tests.cpp` (Hennadii Stepanov)
e550945a39 test, refactor: Remove unused `removed_refs` in `txgraph_tests.cpp` (Hennadii Stepanov)
e50f422d25 test, refactor: Remove unused variables in `test/rbf_tests.cpp` (Hennadii Stepanov)
b7ae50e2e2 fuzz, refactor: Remove unused `header` in `p2p_transport_serialization.cpp` (Hennadii Stepanov)
3df0d067ad fuzz, refactor: Remove unused `random_string` in `locale.cpp` (Hennadii Stepanov)
fc28914de4 fuzz, refactor: Remove unused `linearization` in `cluster_linearize.cpp` (Hennadii Stepanov)
da58e55986 test, refactor: Remove unused `warnings` in `wallet/test/util.cpp` (Hennadii Stepanov)

Pull request description:

  Noted in https://my.cdash.org/builds/3868446/build.

  See commit messages for more details.

  Here is a related upstream change: https://github.com/llvm/llvm-project/pull/203084.

ACKs for top commit:
  maflcko:
    review ACK 3175d57628 🐕

Tree-SHA512: 49334f79aa0effa9bbc94c7bce69bd1869ded87926229e575ba3721108d08ad5b7451222959310773e8e6009125d98016d095ac1a915e2dfa22712c51d8903aa

src/test/fuzz/cluster_linearize.cpp

@@ -611,7 +611,6 @@ FUZZ_TARGET(clusterlin_components)
     // Construct a depgraph.
     SpanReader reader(buffer);
     DepGraph<TestBitSet> depgraph;
-    std::vector<DepGraphIndex> linearization;
     try {
         reader >> Using<DepGraphFormatter>(depgraph);
     } catch (const std::ios_base::failure&) {}

src/test/fuzz/locale.cpp

@@ -45,7 +45,6 @@ FUZZ_TARGET(locale)
     const char* c_locale = std::setlocale(LC_ALL, "C");
     assert(c_locale != nullptr);
 
-    const std::string random_string = fuzzed_data_provider.ConsumeRandomLengthString(5);
     const int64_t random_int64 = fuzzed_data_provider.ConsumeIntegral<int64_t>();
     const std::string tostring_without_locale = util::ToString(random_int64);
     const std::string strprintf_int_without_locale = strprintf("%d", random_int64);

src/test/fuzz/p2p_transport_serialization.cpp

@@ -86,7 +86,6 @@ FUZZ_TARGET(p2p_transport_serialization, .init = initialize_p2p_transport_serial
             assert(msg.m_raw_message_size == CMessageHeader::HEADER_SIZE + msg.m_message_size);
             assert(msg.m_time == time);
 
-            std::vector<unsigned char> header;
             auto msg2 = NetMsg::Make(msg.m_type, std::span{msg.m_recv});
             bool queued = send_transport.SetMessageToSend(msg2);
             assert(queued);