Drop support for Python 3.5 (#4675)

Python 3.5 EOL was on 2020-09-30.

stdlib/3/multiprocessing/managers.pyi

@@ -1,5 +1,3 @@
-# Stubs for multiprocessing.managers
-
 # NOTE: These are incomplete!
 
 import queue
@@ -62,27 +60,16 @@ class Token(object):
 class BaseProxy(object):
     _address_to_local: Dict[Any, Any]
     _mutex: Any
-    if sys.version_info >= (3, 6):
-        def __init__(
-            self,
-            token: Any,
-            serializer: str,
-            manager: Any = ...,
-            authkey: Optional[AnyStr] = ...,
-            exposed: Any = ...,
-            incref: bool = ...,
-            manager_owned: bool = ...,
-        ) -> None: ...
-    else:
-        def __init__(
-            self,
-            token: Any,
-            serializer: str,
-            manager: Any = ...,
-            authkey: Optional[AnyStr] = ...,
-            exposed: Any = ...,
-            incref: bool = ...,
-        ) -> None: ...
+    def __init__(
+        self,
+        token: Any,
+        serializer: str,
+        manager: Any = ...,
+        authkey: Optional[AnyStr] = ...,
+        exposed: Any = ...,
+        incref: bool = ...,
+        manager_owned: bool = ...,
+    ) -> None: ...
     def __deepcopy__(self, memo: Optional[Any]) -> Any: ...
     def _callmethod(self, methodname: str, args: Tuple[Any, ...] = ..., kwds: Dict[Any, Any] = ...) -> None: ...
     def _getvalue(self) -> Any: ...