readdir: Remove unused header include

Since commit c512c691 ("uaccess: implement a proper
unsafe_copy_to_user() and switch filldir over to it") the header file is
no longer needed.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240602101534.348159-2-thorsten.blum@toblux.com


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>