[`fix`] Make Qwen2_5OmniProcessor warning a lot less noisy via warning_once (#45455)
* Make Qwen2_5OmniProcessor warning a lot less noisy via warning_once
* Bonus request: allow fully disabling the warning via config
* Add test to show that warning can be quietened with this
* Revert "Make Qwen2_5OmniProcessor warning a lot less noisy via warning_once"
This reverts commit e20a71fb01db04a039901997a6f0f9acef8d307b to 2ad8a4e3aecb424703288e0067ac353cd7cea463
* Remove system prompt warning
* Make style
* Fully remove apply_chat_template!
* Rerun modular_model_converter.py for qwen3_omni_moe