Use AsyncResult from multiprocessing.pool (#1317)

stdlib/3/multiprocessing/__init__.pyi

@@ -4,6 +4,7 @@ from typing import Any, Callable, Iterable, Mapping, Optional, Dict, List
 
 from multiprocessing.context import BaseContext
 from multiprocessing.managers import SyncManager
+from multiprocessing.pool import AsyncResult
 from multiprocessing.process import current_process as current_process
 
 class Lock():
@@ -12,12 +13,6 @@ class Lock():
     def __enter__(self) -> 'Lock': ...
     def __exit__(self, exc_type, exc_value, tb) -> None: ...
 
-class AsyncResult():
-    def get(self, timeout: float = ...) -> Any: ...
-    def wait(self, timeout: float = ...) -> None: ...
-    def ready(self) -> bool: ...
-    def successful(self) -> bool: ...
-
 class Event(object):
     def __init__(self, *, ctx: BaseContext) -> None: ...
     def is_set(self) -> bool: ...