Consider showing only disallowed licenses in `UpdatedLicences.<repo>.json`

When a new license is detected, the results can sometimes be difficult to parse. Take this result from nuget-client, for example:

```json
{
"files": [
{
"path": "build/NOTICES.txt",
"detected_license_expression": "apache-2.0 AND (apache-2.0 AND unicode-mappings) AND (unicode-mappings AND python) AND bsd-new AND (mit AND x11) AND x11 AND (lgpl-2.0-plus OR cc-sa-1.0) AND bsd-simplified AND mit AND ms-lpl AND apache-1.1 AND (sax-pd AND mit)"
}
]
}
```

The `detected_license_expression` lists many licenses, but the only license that is not listed as an allowed license is `cc-sa-1.0`. It would be helpful if the results instead looked like this:

```json
{
"files": [
{
"path": "build/NOTICES.txt",
"detected_license_expression": "cc-sa-1.0"
}
]
}
```