Ignore datapoint with deleted competitions or deleted users

[Didayolo]

Original PR

• 1662

Description

This fixes the problem where a removed competition are still looked up when measuring, per competition or per user, the size taken in the storage. Those datapoint are now ignored since they are now orphans.

Issues this PR resolves

1654

Checklist

• [x] Code review by me
• [x] Hand tested by me
• [x] I'm proud of my work
• [x] Code review by reviewer
• [x] Hand tested by reviewer
• [x] CircleCi tests are passing
• [x] Ready to merge