reference_format.schema.json: removed from docs but still registered in schema index

[jonathanrobie]

Background

The reference system (a set of fields for describing how Scripture references are formatted in a localized context) was removed from the documentation in commit 3d3b394 as an unimplemented concept. However, reference_format.schema.json still exists and is still registered in schema/index.js:

"referenceFormat": "https://burrito.bible/schema/reference_format.schema.json"
require("./reference_format.schema.json")

Problem

The schema file remains active and registered, which means:

• It can still be used in burritos (validators will accept it)
• It is not documented anywhere in the current spec
• There is no $comment explaining its status

Action needed

Decide whether to:

1. Remove reference_format.schema.json and its registration in index.js entirely (breaking change if anyone uses it)
2. Keep it but add a $comment marking it as unimplemented/deprecated (as was done for recipe)

No known examples use this field.