ci: remove unused Node setup from native builds

[esmuellert]

Summary

Remove unused Node.js setup from the native Linux, macOS, and Windows build workflows.

Changes

• Remove actions/setup-node from _platform-linux.yml
• Remove actions/setup-node from _platform-macos.yml
• Remove actions/setup-node from _platform-windows.yml
• Keep Node.js setup in regression and Copilot workflows where Node programs are actually used
• Keep next PR validation unchanged

Benefits

• Removes the last unused tooling left behind after deleting the manual Node version-bump script
• Reduces setup time and post-job cleanup in six native build cells
• Keeps the native workflows limited to the tools their commands consume

Testing

• The release migration completed successfully across all eight target cells before this cleanup
• The three edited workflows contain no node, npm, or npx command
• YAML parsing passed
• git diff --check passed