Update to address @daira comments wrt fixing configure.ac

Since we're enforcing Boost >= 1.62, we no longer need HAVE_WORKING_BOOST_SLEEP_FOR.

src/utiltime.cpp

@@ -43,20 +43,7 @@ int64_t GetTimeMicros()
 
 void MilliSleep(int64_t n)
 {
-
-/**
- * Boost's sleep_for was uninterruptable when backed by nanosleep from 1.50
- * until fixed in 1.52. Use the deprecated sleep method for the broken case.
- * See: https://svn.boost.org/trac/boost/ticket/7238
- */
-#if defined(HAVE_WORKING_BOOST_SLEEP_FOR)
     boost::this_thread::sleep_for(boost::chrono::milliseconds(n));
-#elif defined(HAVE_WORKING_BOOST_SLEEP)
-    boost::this_thread::sleep(boost::posix_time::milliseconds(n));
-#else
-//should never get here
-#error missing boost sleep implementation
-#endif
 }
 
 std::string DateTimeStrFormat(const char* pszFormat, int64_t nTime)