fix: omit duplicate functions from list of bundled files

[mrstork]

Summary

Recreating #3795

When printing the list of bundled functions, Netlify Build uses zip-it-and-ship-it's listFunctions method, which includes functions that have not been bundled due to a naming conflict (e.g. when both function.js and function.ts are found). Because of this, Netlify Build was incorrectly reporting that both functions were bundled, when in fact only function.js was.

This PR removes those duplicate functions from the list

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[github-actions]

This pull request adds or modifies JavaScript (.js, .cjs, .mjs) files.
Consider converting them to TypeScript.

[github-actions]

This pull request adds or modifies JavaScript (.js, .cjs, .mjs) files.
Consider converting them to TypeScript.