event: replace outdated reactor run loop comment

The work item queueing code was replaced with the current reactor/event
model, but the block comment above _spdk_reactor_run() wasn't updated to
match.  Replace the pseudo-code with something resembling the current
behavior, and delete the outdated paragraph below it.

Change-Id: If0686c6a5d063f56d8ea3df9bf3a1e98eef40207
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>

lib/event/reactor.c

@@ -281,27 +281,19 @@ _spdk_poller_unregister_complete(struct spdk_poller *poller)
 \code
 
 while (1)
-	if (new work items to be scheduled)
+	if (events to run)
-		dequeue work item from new work item ring
+		dequeue and run a batch of events
-		enqueue work item to active work item ring
-	else if (active work item count > 0)
-		dequeue work item from active work item ring
-		invoke work item function pointer
-		if (work item state == RUNNING)
-			enqueue work item to active work item ring
-	else if (application state != RUNNING)
-		# exit the reactor loop
-		break
-	else
-		sleep for 100ms
 
+	if (active pollers)
+		run the first poller in the list and move it to the back
+
+	if (first timer poller has expired)
+		run the first timer poller and reinsert it in the timer list
+
+	if (idle for at least SPDK_REACTOR_SPIN_TIME_US)
+		sleep until next timer poller is scheduled to expire
 \endcode
 
-Note that new work items are posted to a separate ring so that the
-active work item ring can be kept single producer/single consumer and
-only be touched by reactor itself.  This avoids atomic operations
-on the active work item ring which would hurt performance.
-
 */
 static int
 _spdk_reactor_run(void *arg)