[native] Fix new registration flow when not using CSAT

Summary:
This resolves ENG-8055. I broke this while working on ENG-7667.

When I extracted keyserverAuth into useRegistrationServerCall, I made that step a necessary part. I should have considered that we are still supporting !usingCommServicesAccessToken in the new registration, and that the keyserverAuth step should be skipped when !usingCommServicesAccessToken, since auth with the keyserver is handled in the first step.

Test Plan:
First, I backed out of multi-keyserver mode by doing the following:

1. Updating keyserver/secrets/user_credentials.json to set usingIdentityCredentials to false
2. Removing keyserver/facts/authoritative_keyserver.json
3. Removing native/facts/authoritative_keyserver.json
4. Replacing keyserver/secrets/db_config.json so that it points to a DB initialized in a single-keyserver environment
5. Deleted the Android app from my emulator and the iOS app from my simulator

I then tested the following scenarios:

1. On Android, I tested registration as a password user using the legacy registration flow
2. On Android, I tested registration as a password user using the new registration flow
3. On Android, I tested login as a password user
4. On iOS, I tested registration as an Ethereum user using the legacy registration flow (main SIWE button)
5. On iOS, I tested registration as an Ethereum user using the new registration flow
6. On iOS, I tested login as an Ethereum user (main SIWE button)

Reviewers: inka, tomek

Reviewed By: inka

Differential Revision: https://phab.comm.dev/D11926