[identity] reintroduce check to make sure only wallet users can call deleteWalletUser RPC

Summary:
Depends on D12326

Devs will have to pull changes from D12326 to delete password accounts after this change is added to staging

Test Plan: i got a permission denied error trying to call deleteWalletUser from a password account

Reviewers: bartek, will

Reviewed By: will

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12335