[bugfix] fix the complex and potentially problematic generate_kv_idx. (#5957)

### What this PR does / why we need it?
In long-sequence scenarios, the chunked-prefill component may encounter
dimension misalignment issues, which previously occurred during
precision testing on the code_generate_lite dataset. This PR removes
redundant computations and instead derives the value using existing
results and straightforward calculations.
- vLLM version: v0.13.0
- vLLM main:
2c24bc6996

Signed-off-by: QiuChunshuo <qiuchunshuo@huawei.com>

vllm_ascend/worker/model_runner_v1.py

@@ -555,9 +555,6 @@ class NPUModelRunner(GPUModelRunner):
                 self.num_spec_tokens)
 
         if self.pcp_size > 1:
-            if not self.vllm_config.model_config.use_mla:
-                self.pcp_manager.generate_kv_idx(scheduler_output,
-                                                 self.input_batch)
             num_scheduled_tokens[:
                                  num_reqs], position_pcp = self.pcp_manager.update_tokens_for_pcp(
                                      num_scheduled_tokens[:num_reqs],