[Minor] avoid register new custom and just import silly_attn (#28578)

Signed-off-by: Boyuan Feng <boyuan@meta.com>

tests/compile/test_config.py

@@ -15,6 +15,9 @@ from vllm.engine.arg_utils import EngineArgs
 from vllm.platforms import current_platform
 from vllm.utils.torch_utils import _is_torch_equal_or_newer
 
+# This import automatically registers `torch.ops.silly.attention`
+from . import silly_attention  # noqa: F401
+
 
 def test_version():
     # Test the version comparison logic using the private function
@@ -257,15 +260,6 @@ def test_should_split():
     splitting_ops = ["aten::add.Tensor"]
     assert not should_split(node, splitting_ops)
 
-    @torch.library.custom_op(
-        "silly::attention",
-        mutates_args=["out"],
-    )
-    def attention(
-        q: torch.Tensor, k: torch.Tensor, v: torch.Tensor, out: torch.Tensor
-    ) -> None:
-        out.copy_(q + k + v)
-
     q, k, v, out = [torch.randn(1)] * 4
 
     # supports custom ops as OpOverloadPacket