Mark the 1-per-sec update_current_time() call as redundant.

We still do this time update here, since we do it from all
callbacks, but it is no longer a reason to keep the once-per-second
callback enabled.

Closes ticket 26009.

changes/ticket26009

@@ -0,0 +1,9 @@
+  o Minor features (mainloop):
+   - Move responsibility for
+     keeping track of Tor's uptime
+      from a nce-per-second callback to a callback that is only scheduled as
+      needed.  Once enough items are removed from our once-per-second
+      callback, we can eliminate it entirely to conserve CPU when idle.
+      Closes ticket
+      26009.
+

src/or/main.c

@@ -2576,8 +2576,12 @@ second_elapsed_callback(periodic_timer_t *timer, void *arg)
 
   n_libevent_errors = 0;
 
-  /* log_notice(LD_GENERAL, "Tick."); */
   now = time(NULL);
+
+  /* We don't need to do this once-per-second any more: time-updating is
+   * only in this callback _because it is a callback_. It should be fine
+   * to disable this callback, and the time will still get updated.
+   */
   update_current_time(now);
 
   /* the second has rolled over. check more stuff. */