### What this PR does / why we need it? Remove kv_cache nz test case for test_mla_preprocess_nq.py. This case is added by https://github.com/vllm-project/vllm-ascend/pull/3072 but has not been tested on bf16 scenario. Results show that this is not currently supported. ### Does this PR introduce _any_ user-facing change? No ### How was this patch tested? CI passed with existing test. - vLLM version: v0.15.0 - vLLM main: https://github.com/vllm-project/vllm/commit/v0.15.0 Signed-off-by: whx-sjtu <2952154980@qq.com>