refactor(udf): remove function_type field previously used by Deno UDF

[stdrc]

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What's changed and what's your intention?

This PR removes the unused function_type field from all structures related to user-defined functions (#16263). runtime is kept because it seems to be more general, so may be useful in the future.

Checklist

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Release note

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[stdrc]

• refactor(udf): remove function_type field previously used by Deno UDF #19404 👈 (View in Graphite)
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