Deleting existing package.json when `--no-pack` is passed

[Enduriel]

🐛 Bug description

When passing --no-pack to wasm-pack, if an existing package.json is present in the out-dir, it will get deleted

🤔 Expected Behavior

The existing package.json should be left alone, a new one should just not be generated.

👟 Steps to reproduce

Place package.json in /pkg Run wasm-pack build --no-pack

🌍 Your environment

Include the relevant details of your environment. wasm-pack version: 0.13.1 rustc version: 1.91.0-nightly (3672a55b7 2025-08-13)