Describe `Deque` as "output-restricted." (#12285)

* Don't describe `Deque` as "double-ended."

Despite its name, `Deque` is a regular one-way queue. "Double-ended" implies you can add to and remove from either end, which isn't the case.

* Describe `Deque` as "output-restricted."

std/sys/thread/Deque.hx

@@ -27,8 +27,8 @@ package sys.thread;
 #end
 
 /**
-	A Deque is a double-ended queue with a `pop` method that can block until
-	an element is available. It is commonly used to synchronize threads.
+	A Deque is an output-restricted double-ended queue with a `pop` method that can
+	block until an element is available. It is commonly used to synchronize threads.
  */
 @:coreApi extern class Deque<T> {
 	/**