### What this PR does / why we need it? `vanilla_chunked_prefill_mla` and `vanilla_decode_mla` is unused, so remove it. ### Does this PR introduce _any_ user-facing change? ### How was this patch tested? - vLLM version: v0.11.0rc3 - vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0 Signed-off-by: zzzzwwjj <1183291235@qq.com>