Misc: Use C++23 elifdef/elifndef

And drop macros for platforms not supported in the public repo.

src/common/timer.cpp

@@ -374,7 +374,7 @@ void Timer::HybridSleep(std::uint64_t ns, std::uint64_t min_sleep_time)
 
 void Timer::NanoSleep(std::uint64_t ns)
 {
-#if defined(_WIN32)
+#ifdef _WIN32
   HANDLE timer = GetSleepTimer();
   if (timer)
   {
@@ -389,9 +389,6 @@ void Timer::NanoSleep(std::uint64_t ns)
   {
     Sleep(static_cast<std::uint32_t>(ns / 1000000));
   }
-#elif defined(__ANDROID__)
-  // Round down to the next millisecond.
-  usleep(static_cast<useconds_t>((ns / 1000000) * 1000));
 #else
   const struct timespec ts = {static_cast<long>(ns / 1000000000ULL), static_cast<long>(ns % 1000000000ULL)};
   nanosleep(&ts, nullptr);