Expose native fetch_ohttp_keys in every supported downstream language #1362

Since this is removed there is no reason to keep the wrapper function otherwise. I think this whole file can be deleted.

Also, removing this means we should write an expose native fetch_ohttp_keys in every supported downstream language, not just C#.

Originally posted by @spacebear21 in #1354 (comment)

• C# test: fetch ohttp keys #1354
• Python Expose OHTTP key fetch for Python #1386
• Dart Implement native http.fetchOhttpKeys in dart #1495
• JS JS bindings should include io functionality #1250