Remove responsibility for flushing log cbs from mainloop

This is now handled as-needed as the control module is flushing its
own callbacks.  Closes ticket 25951.

changes/ticket25951

@@ -0,0 +1,9 @@
+  o Minor features (mainloop):
+    - Move responsibility for
+      flushing log callbacks
+      from a once-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
+      25951.
+

src/or/main.c

@@ -1701,9 +1701,6 @@ run_scheduled_events(time_t now)
     signewnym_impl(now);
   }
 
-  /* 0c. If we've deferred log messages for the controller, handle them now */
-  flush_pending_log_callbacks();
-
   /* Maybe enough time elapsed for us to reconsider a circuit. */
   circuit_upgrade_circuits_from_guard_wait();