Expose underlying clock in CThreadInterrupt

Overloading sleep_for is not needed, as

* seconds and minutes can be converted to milliseconds by the compiler,
  not needing a duration_cast
* std::condition_variable::wait_for will convert milliseconds to the
  duration type of the underlying clock

So simply expose the clock.

src/threadinterrupt.cpp

@@ -28,18 +28,8 @@ void CThreadInterrupt::operator()()
     cond.notify_all();
 }
 
-bool CThreadInterrupt::sleep_for(std::chrono::milliseconds rel_time)
+bool CThreadInterrupt::sleep_for(Clock::duration rel_time)
 {
     WAIT_LOCK(mut, lock);
     return !cond.wait_for(lock, rel_time, [this]() { return flag.load(std::memory_order_acquire); });
 }
-
-bool CThreadInterrupt::sleep_for(std::chrono::seconds rel_time)
-{
-    return sleep_for(std::chrono::duration_cast<std::chrono::milliseconds>(rel_time));
-}
-
-bool CThreadInterrupt::sleep_for(std::chrono::minutes rel_time)
-{
-    return sleep_for(std::chrono::duration_cast<std::chrono::milliseconds>(rel_time));
-}