gauntlet: fix lint — drop unused subprocess/shutil/tempfile/Path imports

Leftover ffmpeg-era imports from the earlier draft of the CPU transcribe
smoke test; the final numpy-array-bypass version doesn't need them.
Ruff autofix.

tests/test_transcribe.py

@@ -11,11 +11,6 @@ wiring + the SRT contract + the lazy-import path on cheap CPU.
 
 from __future__ import annotations
 
-import os
-import shutil
-import subprocess
-import tempfile
-from pathlib import Path
 
 import pytest