[fully_async] fix: remove invalid rollout.single_turn_response_length override

[Vivicai1005]

What does this PR do?

Removes an invalid Hydra override from the Qwen3.5-35B-A3B fully-async GRPO example script. The line set actor_rollout_ref.rollout.single_turn_response_length, but this key does not exist in RolloutConfig

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Test

No functional code path changes — this only removes a config override that prevented the example script from launching

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[gemini-code-assist]

Code Review

This pull request removes the 'actor_rollout_ref.rollout.single_turn_response_length' configuration parameter from the 'grpo_qwen35_35b_megatron_async.sh' shell script. There are no review comments, and I have no feedback to provide.

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[wuxibin89]

@Vivicai1005 The verl/experimental/fully_async_policy is in maintenance mode, we encourage user to use new V1 trainer:

trainer.use_v1=True
trainer.v1.trainer_mode=colocate_async # sync/colocate_async/separate_async