CLEANUP: task: remove the unused and mishandled global_rqueue_size

This counter is only updated and never used, and in addition it's done
without any atomicity so it's very unlikely to be correct on multi-CPU
systems! Let's just remove it since it's not used.
diff --git a/include/haproxy/task.h b/include/haproxy/task.h
index 24be2b6..41885c2 100644
--- a/include/haproxy/task.h
+++ b/include/haproxy/task.h
@@ -101,7 +101,6 @@
 #ifdef USE_THREAD
 extern struct eb_root timers;      /* sorted timers tree, global */
 extern struct eb_root rqueue;      /* tree constituting the run queue */
-extern int global_rqueue_size; /* Number of element sin the global runqueue */
 #endif
 
 extern struct task_per_thread task_per_thread[MAX_THREADS];
@@ -295,10 +294,9 @@
 {
 	_HA_ATOMIC_SUB(&tasks_run_queue, 1);
 #ifdef USE_THREAD
-	if (t->state & TASK_GLOBAL) {
+	if (t->state & TASK_GLOBAL)
 		_HA_ATOMIC_AND(&t->state, ~TASK_GLOBAL);
-		global_rqueue_size--;
-	} else
+	else
 #endif
 		sched->rqueue_size--;
 	eb32sc_delete(&t->rq);
diff --git a/src/task.c b/src/task.c
index 3336ebc..325fd2e 100644
--- a/src/task.c
+++ b/src/task.c
@@ -50,7 +50,6 @@
 #ifdef USE_THREAD
 struct eb_root timers;      /* sorted timers tree, global */
 struct eb_root rqueue;      /* tree constituting the run queue */
-int global_rqueue_size; /* Number of element sin the global runqueue */
 #endif
 
 static unsigned int rqueue_ticks;  /* insertion count */
@@ -150,7 +149,6 @@
 	eb32sc_insert(root, &t->rq, t->thread_mask);
 #ifdef USE_THREAD
 	if (root == &rqueue) {
-		global_rqueue_size++;
 		_HA_ATOMIC_OR(&t->state, TASK_GLOBAL);
 		HA_SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
 	} else