[SPARK-41916][FOLLOW-UP] Remove unused imports

### What changes were proposed in this pull request?
Remove unused imports

### Why are the changes needed?
clean up

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ci https://github.com/zhengruifeng/spark/actions/runs/20302865798/job/58312749619

### Was this patch authored or co-authored using generative AI tooling?
no

Closes apache#53506 from zhengruifeng/lint2.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Ruifeng Zheng <ruifengz@apache.org>

Author: zhengruifeng

python/pyspark/ml/torch/distributor.py

@@ -18,7 +18,6 @@
 from contextlib import contextmanager
 import collections
 import logging
-import math
 import os
 import random
 import re