[Story] TBC: Remove the /converttodm and /converttoroom

### Story

To be confirmed: since the definition of the DM will be changed so it is only a DM when it has the `m.direct` AND 2 real users, these will not anymore have an effect in all cases and may become rather confusing.

### Dependencies

- TBD

### Sign-offs

#### Android
- [ ] Design sign-off on completion
- [ ] QA sign-off on completion
- [ ] Product sign-off on completion

#### iOS
- [ ] Design sign-off on completion
- [ ] QA sign-off on completion
- [ ] Product sign-off on completion

#### Web
- [ ] Design sign-off on completion
- [ ] QA sign-off on completion
- [ ] Product sign-off on completion

### Scope

```[tasklist]
### Android
- [ ] Verified with build in screen reader
```

```[tasklist]
### iOS
- [ ] Verified with build in screen reader
```

```[tasklist]
### Web
- [ ] Verified with system in screen reader
```

## Out of scope

- TBD

The issue names the /converttodm and /converttoroom endpoints but provides no files, tests, or implementation entry points. First confirm the dependency and whether removal is required across Android, iOS, and Web, then locate each client's endpoint handling. Done means the confirmed scope is removed and the listed design, QA, product, and screen-reader checks are completed.

Written by the indexing model from the issue text.