[lib][native] update useDeleteDiscardedIdentityAccount to call deletePasswordUser when appropriate

Summary: in a later diff, we'll be restricting deleteWalletUser to only be called by wallet accounts. before then, we need username accounts to call deletePasswordUser instead.

Test Plan: tried registering a wallet and password user with my authoritative keyserver offline. confirmed in CloudWatch logs that both accounts were successfully registered and then subsequently deleted when keyserver auth failed. checked that the correct RPC was called each time

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D12325