feat: remove usage data

Author: fridayL

src/memos/api/routers/server_router.py

@@ -299,6 +299,7 @@ def _format_memory_item(memory_data: Any) -> dict[str, Any]:
     memory["ref_id"] = ref_id
     memory["metadata"]["embedding"] = []
     memory["metadata"]["sources"] = []
+    memory["metadata"]["usage"] = []
     memory["metadata"]["ref_id"] = ref_id
     memory["metadata"]["id"] = memory_id
     memory["metadata"]["memory"] = memory["memory"]