Removed imported symbols that are not accessed or re-exported (#4387)

Co-authored-by: Eric Traut <erictr@microsoft.com>

stdlib/3/collections/__init__.pyi

@@ -1,4 +1,3 @@
-# These are not exported.
 import sys
 import typing
 from typing import (
@@ -37,9 +36,6 @@ from typing import (
     overload,
 )
 
-# These are exported.
-from . import abc
-
 if sys.version_info >= (3, 6):
     from typing import AsyncGenerator as AsyncGenerator, Collection as Collection