`--all` doesn't work or docs are incorrect

```
>dotnet-core-uninstall --version
1.5.255402+e07a3c995ec2d3cf449d37eb50c87e180da12544
```

If I read the help correctly, `--all` is supposed to remove everything:
```
Usage:
dotnet-core-uninstall remove [options] [...]

Arguments:
The specified version to uninstall. You may list several versions. Response files are supported.

Options:
--all Remove all .NET Core SDKs or Runtimes. (*)
... < snip > ...
```

... however, when I run it I get the following error:
```
>dotnet-core-uninstall remove --all
You must specify exactly one of: --aspnet-runtime, --hosting-bundle, --runtime, --sdk.
```