fix: simplify `legacyToJSON` #723

Job	Run time
prepare	15s
generate (legacy-json, ./node/doc/api/*.md, object-assertion)	33s
generate (api-links, ./node/lib/*.js, object-assertion)	32s
generate (man-page, ./node/doc/api/cli.md)	25s
generate (addon-verify, ./node/doc/api/addons.md)	30s
generate (legacy-html, ./node/doc/api/*.md, file-size)	46s
generate (web, ./node/doc/api/*.md, file-size)	1m 7s
generate (llms-txt, ./node/doc/api/*.md, file-size)	38s
generate (orama-db, ./node/doc/api/*.md, file-size)	36s
generate (json-simple, ./node/doc/api/*.md)	35s
	5m 57s

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