The output of 'arc linters' no longer correctly differentiates configured linters from available ones.
Having traced this through a little, it looks like the 'built_linters' array at https://secure.phabricator.com/diffusion/ARC/browse/master/src/lint/engine/ArcanistConfigurationDrivenLintEngine.php$46 does not get any entries as '$this->getPaths()' is empty in the Linters workflow.
It feels like the presence or otherwise of a linter should probably not depend on the paths at all.
Steps to reproduce:
Create a .arclint file with the following contents:
```
{
"linters": {
"generated": {
"type": "generated"
}
}
}
```
Expected output from 'arc linters':
```
CONFIGURED generated (Generated Code)
```
Actual output:
```
AVAILABLE generated (Generated Code)
```