Remove unecessary is_fa3_supported check (sgl-project#6112)

Author: hebiao064

sgl-kernel/python/sgl_kernel/flash_attn.py

@@ -144,10 +144,6 @@ def flash_attn_with_kvcache(
             logsumexp of each row of the matrix QK^T * scaling (e.g., log of the softmax
             normalization factor).
     """
-    if not is_fa3_supported():
-        raise NotImplementedError(
-            "flash_attn at sgl-kernel is only supported on sm90 and cu123 above"
-        )
     assert k_cache.stride(-1) == 1, "k_cache must have contiguous last dimension"
     assert v_cache.stride(-1) == 1, "v_cache must have contiguous last dimension"
     if softmax_scale is None: