remove _os_alt_seps

src/flask/helpers.py

@@ -18,13 +18,6 @@ from .globals import request
 from .globals import session
 from .signals import message_flashed
 
-# what separators does this operating system provide that are not a slash?
-# this is used by the send_from_directory function to ensure that nobody is
-# able to access files from outside the filesystem.
-_os_alt_seps = list(
-    sep for sep in [os.path.sep, os.path.altsep] if sep not in (None, "/")
-)
-
 
 def get_env():
     """Get the environment the app is running in, indicated by the