[Bugfix] Fix disaggregated pd error

[Potabk]

What this PR does / why we need it?

Fix ascend_env has no attr VLLM_ASCEND_ENABLE_CHUNK_MC2, remove useless lines

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.10.0
• vLLM main: vllm-project/vllm@9edd1db

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.70%. Comparing base (875a86c) to head (f232d08).
⚠️ Report is 618 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2242   +/-   ##
=======================================
  Coverage   76.70%   76.70%           
=======================================
  Files         113      113           
  Lines       12944    12944           
=======================================
  Hits         9929     9929           
  Misses       3015     3015           

Flag	Coverage Δ
unittests	76.70% <ø> (ø)

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