full cudagraph for flex-attn (#36298)

Signed-off-by: shunting314 <shunting@meta.com>

tests/compile/fullgraph/test_full_cudagraph.py

@@ -170,14 +170,3 @@ class TestFullCUDAGraph:
                 piecewise_res.outputs[0].text.lower()
                 == full_res.outputs[0].text.lower()
             )
-
-
-@pytest.mark.skipif(not current_platform.is_cuda(), reason="Skip if not cuda")
-def test_full_cudagraph_with_invalid_backend():
-    # Flex_Attention is not supported with full cuda graph
-    with pytest.raises(RuntimeError):
-        LLM(
-            model="Qwen/Qwen2-1.5B-Instruct",
-            compilation_config=CompilationConfig(cudagraph_mode="FULL"),
-            attention_config={"backend": "FLEX_ATTENTION"},
-        )