OCM. delete-accepted-user endpoint always returns 200

```
Web UI 10.3.0
Ocis: 6.5.0
```

Steps:
`Given using server "LOCAL"`
`And "Alice" has generated invitation`
`And using server "REMOTE"`
`And "Brian" has accepted invitation`
`And "Brian" deletes connection to user "Alice"`

Actual: 200. Should be 204?

`And "Brian" tries to delete connection to user "Alice"` - or use random userId

Expected: bad request. user not found
Actual: 200