What this PR does / why we need it?

This PR simplifies the DeepSeek-V4 CSA and MHC implementations after the Ascend fused paths became stable.

Main changes:

• Remove redundant Triton MHC, Sinkhorn, RMSNorm, and SFA implementations.
• Retain the Triton pre_only kernel required by the MHC head stage.
• Keep eager implementations as fallback paths.
• Rename G2-related components to DeepSeek-V4 CSA/HCA terminology.
• Relocate MHC operators into the common ops directories.
• Consolidate CSA eager attention implementations.
• Align DeepSeek-V4 CLI arguments with Megatron and MindSpeed conventions.
• Remove incompatible legacy RoPE options from all DeepSeek-V4 scripts.

Does this PR introduce any user-facing change?

Yes. DeepSeek-V4 CLI configurations need to be updated as follows:

Recommended DeepSeek-V4 position embedding configuration:

--position-embedding-type deepseek4
--qk-pos-emb-head-dim 64

Do not combine it with:

--use-fused-rotary-pos-emb
--use-rotary-position-embeddings

How was this patch tested?

• Checked all DeepSeek-V4 training, fine-tuning, inference, POC, and ST scripts.
• Verified that removed CLI options have no remaining DeepSeek-V4 references.
• Ran bash -n against all affected DeepSeek-V4 shell scripts.
• Ran Python compilation and applicable code-quality checks for the modified Python modules.
• Ran git diff --check.
• Applicable local pre-commit hooks passed. The local Gitleaks hook could not run because the ./gitleaks binary was unavailable.
• GitCode remote Git Hooks passed successfully.
• Verified that importing the repository without Triton remains protected by the existing try/except logic.