[UX] Rename CUTLASS_MLA_VLLM_V1 to CUTLASS_MLA

[mgoin]

We should probably remove most of the "VLLM_V1" attention names and just use their base name + use_v1

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[gemini-code-assist]

Code Review

This pull request correctly renames CUTLASS_MLA_VLLM_V1 to the more concise CUTLASS_MLA across several files. The changes are consistent and improve code clarity. I've identified one pre-existing but relevant issue in the logic that handles this backend selection, which could lead to silent fallbacks and unexpected behavior. My review includes a suggestion to make this behavior more explicit by raising an error on misconfiguration.

[yewentao256]

Looks good to me

[alexm-redhat]

thanks for doing this!