Wrong error response code when trying to delete a non existing link over a space

## Describe the bug

A `DELETE` request over a non-existing link (removed before) returns a `400 Bad Request` error code. It should be a `404 Not found`

## Steps to reproduce

I use the Android client

1. In a space with several links, open `Members`
2. In web, remove any on the links
3. In app, remove the already removed link

This is the curl command

```
curl -H 'User-Agent: Mozilla/5.0 (Android) ownCloud-android/4.7.0' -H 'Accept-Language: en' -H 'Authorization: Bearer 'xxx' -H 'Connection: Keep-Alive' -H 'content-length: 0' -X DELETE 'https://xx.xx.xx.xx:9200/graph/v1beta1/drives//root/permissions/uuNBicMytEAbtOA'
```

## Expected behavior

Backed should return a `404`

## Actual behavior

App shows an `unknown` error because the `400` code

## Setup