[main] remove dbo code (#3712)

### What this PR does / why we need it?
Remove codes of dbo.
Currently, vLLM has supported dbo with pr:
https://github.com/vllm-project/vllm/pull/23693.

### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.11.0rc3
- vLLM main:
17c540a993

Signed-off-by: zzzzwwjj <1183291235@qq.com>

vllm_ascend/utils.py

@@ -758,13 +758,13 @@ def get_default_buffer_config() -> dict:
 def calculate_dp_buffer_size() -> int:
     """
     formula of dp buffer size:
-    dp_size + 2 (flags: with_prefill and enable_dbo)
+    dp_size + 1 (flags: with_prefill)
     """
     from vllm.config import get_current_vllm_config
     vllm_config = get_current_vllm_config()
     dp_size = vllm_config.parallel_config.data_parallel_size
     int32_size = torch.iinfo(torch.int32).bits // 8
-    dp_buffer_size = math.ceil((dp_size + 2) * int32_size / (1024 * 1024))
+    dp_buffer_size = math.ceil((dp_size + 1) * int32_size / (1024 * 1024))
     return max(dp_buffer_size, _MIN_DP_BUFFER_SIZE)