[CI][BugFix][AMD] Don't set VLLM_ROCM_USE_AITER anymore in test_rocm_aiter_topk since its not necessary (#36996)

Signed-off-by: Randall Smith <Randall.Smith@amd.com>

tests/kernels/moe/test_rocm_aiter_topk.py

@@ -10,7 +10,6 @@
 # and the platform is not ROCm.
 
 import importlib.util
-import os
 
 import pytest
 import torch
@@ -20,9 +19,6 @@ from vllm.platforms import current_platform
 if not current_platform.is_rocm():
     pytest.skip("This test can only run on ROCm.", allow_module_level=True)
 
-# This environment variable must be set so ops will be registered.
-os.environ["VLLM_ROCM_USE_AITER"] = "1"
-
 # this import statement is needed to ensure the ops are registered
 import vllm.model_executor.layers.fused_moe.rocm_aiter_fused_moe  # noqa: F401