remove @unittest.skip in test_parallel_executor_mnist.py (#22019)

python/paddle/fluid/tests/unittests/test_parallel_executor_mnist.py

@@ -175,9 +175,6 @@ class TestMNIST(TestParallelExecutorBase):
             for use_fast_executor in (False, True):
                 self.check_batchnorm_fc_convergence(use_cuda, use_fast_executor)
 
-    # FIXME(wuyi): should checkout why this fails when merging
-    # https://github.com/PaddlePaddle/Paddle/pull/16545
-    @unittest.skip("should fix this later")
     def test_batchnorm_fc_with_new_strategy(self):
         # NOTE: the computation result of nccl_reduce is non-deterministic,
         # related issue: https://github.com/NVIDIA/nccl/issues/157