Broken master due to `rspec:feature-flags`

Job #816109505 failed for 72c424e8:

These feature flags appears to be UNUSED
If they are really no longer needed REMOVE their .yml definition
If they are needed you need to ENSURE that their usage is covered with specs to continue.
- admin_approval_for_new_user_signups
Feature flag usage check failed.

Flag usage was removed by !46051 (diffs).