Revert "Merge pull request #2893 from dimagi/add-billing-admins"

This reverts commit 54e9cb3704686c5297fc59ec20b5dd6e010aea63, reversing
changes made to 729e74c30a3fe476fd7dec02e657833ba86c4ed0.
Merge pull request #2895 from dimagi/migration-revert

Revert "Merge pull request #2893 from dimagi/add-billing-admins"