Resolve "uncategorized" apphost 3.1.18 prebuilt for the roslyn repo for 6.0

The following "uncatergorized" prebuilts are coming from roslyn. They can be seen in the repo's prebuilt-report. The project location of where these come from is unknown.

```
<Usage Id="Microsoft.NETCore.App.Host.linux-x64" Version="3.1.18" />
```