MINOR: applet: rename applet_runq to applet_active_queue

This is not a real run queue and we're facing ugly bugs because
if this : if a an applet removes another applet from the queue,
typically the next one after itself, the list iterator loops
forever because the list's backup pointer is not valid anymore.
Before creating a run queue, let's rename this list.
diff --git a/src/haproxy.c b/src/haproxy.c
index 465bb6a..a20f497 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -1524,7 +1524,7 @@
 			break;
 
 		/* expire immediately if events are pending */
-		if (fd_cache_num || run_queue || signal_queue_len || !LIST_ISEMPTY(&applet_runq))
+		if (fd_cache_num || run_queue || signal_queue_len || !LIST_ISEMPTY(&applet_active_queue))
 			next = now_ms;
 
 		/* The poller will ensure it returns around <next> */