Remove "Delete tenant" functionality

Continuation of https://github.com/oaeproject/3akai-ux/issues/3718.

The "Delete Tenant" functionality has been removed from the UI in the User Management work. The functionality should now also be removed from Hilary.
We should provide a migration to drop the `deleted` column from the Tenants CF and remove it from the createColumnFamilies call in `init.js`