refactor(plugins): drop unused sherpa-onnx wave FFI bindings

[staging-devin-ai-integration]

Summary

• Delete the SherpaOnnxWave struct and the SherpaOnnxReadWave / SherpaOnnxFreeWave externs from the sensevoice plugin's FFI module. They had no callers and were retained only by "kept for future use" comments plus #[allow(dead_code)]; the plugin receives decoded f32 frames and never reads wave files.
• Shrinks the unsafe FFI surface a reader has to reason about. No behavior change.
• The unused #[repr(C)] per-model config structs are intentionally left alone — they are required for SherpaOnnxOfflineModelConfig's ABI layout.

Review & Validation

• Confirm nothing outside the plugin referenced the removed symbols (cargo clippy --all-targets in plugins/native/sensevoice passes clean).

Link to Devin session: https://staging.itsdev.in/sessions/b70e5ce2bbc7403ca8f026cf2b1d820b
Open in Devin Desktop: https://staging.itsdev.in/desktop/session/b70e5ce2bbc7403ca8f026cf2b1d820b?variant=devin-insiders
Requested by: @streamer45

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Devin Review

Status	Commit
🟢 Reviewed	53f57fa

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[staging-devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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