Merge bitcoin/bitcoin#34926: test: Replace DEBUG_LOG_OUT with -printtoconsole=1

261d229455 test: Replace DEBUG_LOG_OUT with -printtoconsole=1 (Hodlinator)

Pull request description:

  `-printtoconsole=1` has the same functionality but works in more cases than `DEBUG_LOG_OUT`, so remove the latter (`-printtoconsole` is already used when fuzzing). This means we can drop `G_TEST_LOG_FUN`.

  ---
  Behavior can be verified through
  ```shell
  ctest --test-dir build --debug
  ```
  and checking for:
  ```
  142: Test command: /home/hodlinator/bc/2/build/bin/test_bitcoin "--run_test=coinselector_tests" "--catch_system_error=no" "--log_level=test_suite" "--" "-printtoconsole=1"
  ...
  142: 2026-03-26T13:40:02.169392Z [test] [../src/kernel/context.cpp:20] [operator()] Using the 'sse4(1way);sse41(4way);avx2(8way)' SHA256 implementation
  ```

  ---
  Inspired by: https://github.com/bitcoin/bitcoin/pull/34918#discussion_r2994780532

ACKs for top commit:
  nkatha23:
    ACK 261d229
  maflcko:
    review ACK 261d229455 📬
  kevkevinpal:
    crACK [261d229](261d229455)
  janb84:
    cr ACK 261d229455

Tree-SHA512: f4c793b4a00730ade113241baeaaef08ae0333df15ada5929dd46aacd1ac875733e58aa341fac8fb5875eb5ebca735d40c664bf0ef62132094e0c993da5b20e5

src/test/fuzz/fuzz.cpp

@@ -37,8 +37,6 @@
 __AFL_FUZZ_INIT();
 #endif
 
-const std::function<void(const std::string&)> G_TEST_LOG_FUN{};
-
 /**
  * A copy of the command line arguments that start with `--`.
  * First `LLVMFuzzerInitialize()` is called, which saves the arguments to `g_args`.