[V0 deprecation] Remove _set_default_args_v0 function

[Isotr0py]

Purpose

• Remove _set_default_args_v0 since v0 engine has been removed

Test Plan

Test Result

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request removes the _set_default_args_v0 function and related logic as part of the V0 engine deprecation. The changes are straightforward, renaming _set_default_args_v1 to _set_default_args and simplifying the call site. However, the removal of V0 components appears to be incomplete in other parts of the codebase. I've pointed out a critical issue where setting VLLM_USE_V1=0 could lead to a runtime crash due to lingering references to V0 components in platform-specific files. This should be addressed to ensure the V0 removal is clean and does not introduce new bugs.

[gemini-code-assist]

While this change correctly removes the V0-specific default arguments, the removal of V0 components seems incomplete across the codebase. Several platform-specific files still contain logic that depends on VLLM_USE_V1 and might attempt to use V0 components, which are presumably removed. This could lead to runtime errors if a user sets VLLM_USE_V1=0.

For example, in vllm/platforms/cuda.py and vllm/platforms/rocm.py, the code still selects vllm.worker.worker.Worker if VLLM_USE_V1 is false. If this V0 worker has been removed, this will cause a crash.

It is recommended to update these files to either always use the V1 worker or raise an error if VLLM_USE_V1=0, similar to the approach in cpu.py, xpu.py, and tpu.py which explicitly disallow VLLM_USE_V1=0.