message: test: Replace boost::mutex with std::mutex
diff: #include <boost/test/unit_test.hpp>
  #include <boost/thread.hpp>
  +#include <mutex>
  +
  BOOST_AUTO_TEST_SUITE(scheduler_tests)
  -static void microTask(CScheduler& s, boost::mutex& mutex, int& counter, int delta, std::chrono::system_clock::time_point rescheduleTime)
  +static void microTask(CScheduler& s, std::mutex& mutex, int& counter, int delta, std::chrono::system_clock::time_point rescheduleTime)
  {
  {
  - boost::unique_lock<boost::mutex> lock(mutex);
  + std::lock_guard<std::mutex> lock(mutex);
  counter += delta;
  }
  std::chrono::system_clock::time_point noTime = std::chrono::system_clock::time_point::min();
  @@ -38,7 +40,7 @@ BOOST_AUTO_TEST_CASE(manythreads)
  // counters should sum to the number of initial tasks performed.
  CScheduler microTasks;
  - boost::mutex counterMutex[10];
  + std::mutex counterMutex[10];
  int counter[10] = { 0 };
  FastRandomContext rng{/* fDeterministic */ true};
  auto zeroToNine = [](FastRandomContext& rc) -> int { return rc.randrange(10); }; // [0, 9]
  