Right now it's using php 7.0, so we had to disable the master db upgrade comparison job recently and also, some false linting problems are being reported with features only available in 7.1 and up.
So the idea is:
1) Upgrade integration.moodle.org to use PHP 7.1
2) Remove the 31_STABLE jobs from it. That branch falls out of support in May 2019 and we have the 2 CI laptops covering it. So NP, so far.
3) Enable back the master db upgrade comparison job job.
4) Verify that this is not reported anymore.