[Refactor] Remove the process patches of Qwen2.5-VL and Qwen2.5-Omni

[gcanlin]

What this PR does / why we need it?

Related to #4084. Before we add the patches temporarily for making set_forward_context patched by set_ascend_forward_context in the function _process_image_input and _process_video_input of Qwen2.5-VL and Qwen2.5-Omni models. After removing these patches, I met the AttributeError for ForwardContext missing prefetch_mlp_enabled. So we need to add the defensive check for prefetch_mlp_enabled.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

vllm serve Qwen/Qwen2.5-VL-7B-Instruct \
    --max-model-len 30000 \
    --max-num-batched-tokens 50000 \
    --max-num-seqs 30 \
    --no-enable-prefix-caching \
    --trust-remote-code \
    --dtype bfloat16

{"id":"chatcmpl-b66d8acb76905c49","object":"chat.completion","created":1765796863,"model":"/root/.cache/modelscope/hub/models/Qwen/Qwen2.5-VL-7B-Instruct","choices":[{"index":0,"message":{"role":"assistant","content":"The text in the illustration reads \"TONGYI Qwen.\"","refusal":null,"annotations":null,"audio":null,"function_call":null,"tool_calls":[],"reasoning":null,"reasoning_content":null},"logprobs":null,"finish_reason":"stop","stop_reason":null,"token_ids":null}],"service_tier":null,"system_fingerprint":null,"usage":{"prompt_tokens":73,"total_tokens":88,"completion_tokens":15,"prompt_tokens_details":null},"prompt_logprobs":null,"prompt_token_ids":null,"kv_transfer_params":null}

• vLLM version: v0.12.0
• vLLM main: vllm-project/vllm@ad32e3e

[gemini-code-assist]

Code Review

This pull request refactors the codebase by removing temporary patches for the Qwen2.5-VL and Qwen2.5-Omni models. These patches were responsible for setting an Ascend-specific forward context. Their removal led to an AttributeError due to the prefetch_mlp_enabled attribute being accessed without being set. The pull request addresses this by defensively accessing the attribute using getattr with a default value. This is a clean and robust solution that improves code maintainability by removing temporary workarounds and preventing potential runtime errors. The changes are correct and well-implemented.

[github-actions]

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[shen-shanshan]

LGTM, thanks~