refactor: removed mention of js polyfills that are not used any more

[ecreeth]

Summary

Both JSC and hermes implements these methods, so we aren't using a polypill version of them.

• Array.from
• Array.prototype.includes
• Array.prototype.{find, findIndex}
• Object.{entries, values}
• Object.assign
• String.prototype.{startsWith, endsWith, repeat, includes}

See string-functions, object-functions and array-functions for reference.

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