Bump stable IREE version for sgl-benchmark (#757)

# Description

[SGLang Benchmark
Test](https://github.com/nod-ai/shark-ai/actions/workflows/ci-sglang-benchmark.yml)
has been failing at the compilation step. Bumping IREE version to the
stable versions pushed in #721 fixes the issue.

Author: stbaione

.github/workflows/ci-sglang-benchmark.yml

@@ -70,8 +70,8 @@ jobs:
 
           # Pin to known-working versions.
           pip install -f https://iree.dev/pip-release-links.html --pre --upgrade \
-            iree-base-compiler==3.1.0rc20241204 \
-            iree-base-runtime==3.1.0rc20241204 \
+            iree-base-compiler==3.1.0rc20241220 \
+            iree-base-runtime==3.1.0rc20241220 \
             "numpy<2.0"
 
           # Install SGLang

app_tests/benchmark_tests/llm/sglang_benchmarks/shortfin_benchmark_test.py

@@ -7,7 +7,6 @@
 import logging
 import multiprocessing
 import os
-from pathlib import Path
 import pytest
 import time
 from unittest.mock import patch