allow a timeout of a full 'unit'

the -1 in the FbTk::FbTimer::remainingNext() function was pointless in the
first place anyway: reducing the timeout by just 1 microsecond improves
nothing (in this case). if the timer triggers exactly at a full unit (second)
then it's correct to wait for the full next unit.

src/FbTk/FbTime.hh

@@ -47,7 +47,7 @@ namespace FbTime {
     // calculates the remaining microseconds from 'now' up to the
     // next full 'unit'
     inline uint64_t remainingNext(uint64_t now, uint64_t unit) {
-        return (unit - (now % unit) - 1);
+        return (unit - (now % unit));
     }
 
 } // namespace FbTime