It is currently possible to delete an artifact that is associated with a workflow run using the GitHub API: https://developer.github.com/v3/actions/artifacts/#delete-an-artifact

This API is limited though because an artifact is not available until after a run is complete

The @actions/artifact package should add a public deleteArtifact() method that will allow users to delete an artifact during a run

This will make it easier to support certain types types of scenarios such as retention