Revert "logreader.py: concurrent file existence checks (#34875)"

This reverts commit e11b239b2e.

tools/lib/logreader.py

@@ -13,7 +13,6 @@ import warnings
 import zstandard as zstd
 
 from collections.abc import Callable, Iterable, Iterator
-from concurrent.futures import ThreadPoolExecutor, as_completed
 from urllib.parse import parse_qs, urlparse
 
 from cereal import log as capnp_log
@@ -202,15 +201,9 @@ def direct_source(file_or_url: str) -> list[LogPath]:
 
 
 def get_invalid_files(files):
-  if not files:
-    return
-
-  with ThreadPoolExecutor(max_workers=32) as executor:
-    future_to_file = {executor.submit(file_exists, file): file for file in files}
-    for future in as_completed(future_to_file):
-      file = future_to_file[future]
-      if not future.result():
-        yield file
+  for f in files:
+    if f is None or not file_exists(f):
+      yield f
 
 
 def check_source(source: Source, *args) -> list[LogPath]: