Cleanup tl.constexpr HAS_ATTN_SCALE (#2531)

Summary:
X-link: meta-recsys/generative-recommenders#110

Pull Request resolved: #2531

Reviewed By: LinjianMa

Differential Revision: D65366330

fbshipit-source-id: 43be8c6a04a8751749c35cd18f79a92046e5d36b

Author: hanli0612

torchbenchmark/operators/ragged_attention/hstu.py

@@ -117,8 +117,7 @@ def forward(
             "ALLOW_TF32": True,
             "BLOCK_D_Q": DimQ,
             "BLOCK_D_V": DimV,
-            "max_attn_len": 0,
-            "HAS_MAX_ATTN_LEN": False,
+            "MAX_ATTN_LEN": 0,
             "sort_by_length_indices": False,
             "AUTOTUNE_MAX_SEQ_LEN": N,
             "contextual_seq_len": 0,