fix: remove duplicate agrupar_por_factura that was overriding the correct one

The second definition (for RIPS 2.0 transacción grouping) was never called
but silently overrode the CMXC ventas grouper, causing grupos_vta to always
be empty (values were dicts, not lists, so isinstance(v, list) was False).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/services/json_generator.py

@@ -378,16 +378,6 @@ def generar_procedimiento(row: dict, consecutivo: int) -> dict:
     }
 
 
-def agrupar_por_factura(rows: list, factura_default: str = "") -> dict:
-    grupos = defaultdict(lambda: {"factura": "", "procedimientos": []})
-    for row in rows:
-        doc_key = (row.get("tipo_doc_paciente", "CC"), row.get("num_doc_paciente", ""))
-        fact = row.get("num_factura", factura_default)
-        grupos[(fact, doc_key)]["factura"] = fact
-        grupos[(fact, doc_key)]["procedimientos"].append(dict(row))
-    return grupos
-
-
 def generar_transaccion(
     factura: str,
     num_doc_obligado: str,