[Python] python/benchmarks/parquet.py has flake8 failures

### Describe the bug, including details regarding any error messages, version, and platform.

```text
/arrow/python/benchmarks/parquet.py:18:1: F401 'shutil' imported but unused
/arrow/python/benchmarks/parquet.py:19:1: F401 'tempfile' imported but unused
/arrow/python/benchmarks/parquet.py:23:1: F401 'pandas as pd' imported but unused
```

### Component(s)

Python