[ROCm] Remove Triton dispatch for blockscale FP8 GEMM

[samremes]

The AITER CK/CKTile blockscale GEMM path now supports split-K tuning, which matches or exceeds Triton performance across all shapes. Remove the conditional Triton dispatch (is_triton_gemm_w8a8_tuned + triton_gemm_a8w8_blockscale) from the ROCm AITER path and always use the CK-backed gemm_a8w8_blockscale.

This simplifies the dispatch logic, removes the hardcoded tuned-shapes list, and eliminates the Triton-specific quantization path in _run_aiter.

Made-with: Cursor

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[samremes]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Merge conflicts resolved in commit 230302e. The key changes:

• vllm/_aiter_ops.py: Kept the new preshuffled per-token W8A8 gemm functions added in upstream; dropped the _rocm_aiter_triton_gemm_a8w8_blockscale_impl/fake functions that our PR removed.
• vllm/model_executor/layers/quantization/utils/fp8_utils.py: Accepted upstream's version — the W8A8BlockFp8LinearOp class was refactored out in a separate upstream commit.
• vllm/model_executor/kernels/linear/scaled_mm/aiter.py: Applied the same Triton dispatch removal intent to the new AiterFp8BlockScaledMMKernel class (where the logic was moved by upstream's refactor), dropping use_triton / is_triton_gemm_w8a8_tuned and always using rocm_aiter_ops.gemm_a8w8_blockscale.