deprecation of CIS-DI-0005

**Description**

```
"code": "CIS-DI-0005",
"title": "Enable Content trust for Docker",
"level": "INFO",
"alerts": [
    "export DOCKER_CONTENT_TRUST=1 before docker pull/build"
 ]
```

**What did you expect to happen?**
No alert, since this property has been deprecated, see:
https://www.docker.com/blog/retiring-docker-content-trust/

**What happened instead?**
Dockle reports as an (INFO) alert
