[Misc] Removes unnecessary graph size re-initialization (#6280)

### What this PR does / why we need it?

This PR removes `update_default_aclgraph_sizes`. In earlier versions, we
add this function to change default `cudagraph_capture_sizes` because
`_npu_paged_attention` degrades significantly on certain shapes (which
is included in default `cudagraph_capture_sizes` of VLLM). Now since we
use FIA as default attention op (which does not contain such performance
degradation), there is no need to add this default change. Otherwise, it
could cause some conflicts if we set a small `cudagraph_capture_sizes`
that < 20 now.

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

### How was this patch tested?

- vLLM version: v0.14.1
- vLLM main:
d68209402d

---------

Signed-off-by: Angazenn <supperccell@163.com>

vllm_ascend/platform.py

@@ -47,7 +47,6 @@ from vllm_ascend.utils import (
     refresh_block_size,
     update_aclgraph_sizes,
     update_cudagraph_capture_sizes,
-    update_default_aclgraph_sizes,
     is_310p,
 )
 
@@ -247,10 +246,6 @@ class NPUPlatform(Platform):
 
         # set cudaprah sizes before extending `compilation_config.splitting_ops`
         vllm_config._set_cudagraph_sizes()
-        # There are cases where default cudagraph_capture_sizes are not friendly
-        # to ascend ops && hardwares. We update these sizes here to improve
-        # default performance.
-        update_default_aclgraph_sizes(vllm_config)
         # TODO delete graph size update here when compilation_config.pass_config.enable_sp
         # is supported by vllm-ascend.
         if (