title: Delete or reset Gitlab CI builds
body: <p>Is it possible to delete old builds in Gitlab CI?
  I tested a few things and have now about 20 builds that are useless (most are failed anyway).
  It also shows stages that I don't have anymore which kinda clutters the Pipelines page and some of the uploaded artifacts are a bit big.</p>
  
  <p>I wasn't able to find any documentation on this, only that disabling CI in the settings doesn't remove the builds.</p>
  
  <p>Using Gitlab 8.10 Community (hosted by Gitlab.com)</p>