sched: Move timer dispatch loop to board code

Rename sched_timer_kick() to sched_timer_dispatch() and move its loop
into its callers in the board code.  This eliminates the need to
export timer_try_set_next() from the board code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/main.c

@@ -75,12 +75,6 @@ timer_read_time(void)
     return 0; // XXX
 }
 
-uint8_t
-timer_try_set_next(unsigned int next)
-{
-    return 1;
-}
-
 
 /****************************************************************
  * Turn stdin/stdout into serial console