ruff linting/Python 3.10 cleanup

src/ocrmypdf/optimize.py

@@ -11,11 +11,10 @@ import sys
 import tempfile
 import threading
 from collections import defaultdict
-from collections.abc import Iterator, MutableSet, Sequence
+from collections.abc import Callable, Iterator, MutableSet, Sequence
 from os import fspath
 from pathlib import Path
-from typing import Any, Callable, NamedTuple, NewType
-from warnings import warn
+from typing import Any, NamedTuple, NewType
 from zlib import compress
 
 import img2pdf