No obj_text for triples that stores logical forms for chats

## Type of Issue

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- [ ] Bug report (to report a bug)
- [ ] Feature request (to request an additional feature)
- [ ] Tracker (I am just using this as a tracker)
- [ ] Refactor request
- [ ] Documentation Ask

## Description

Triples that stores logical forms of chats now only have `obj (mem_id)`, the `obj_text` field is always None. This is okay because we can also get `mem_id` first then use `mem_id` to get logical form, but wouldn't it be better if we also store logical form as `obj_text`?