fix(ras-acc): clear RAS user tokens on logout

[chickenn00dle]

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Changes proposed in this Pull Request:

Closes https://app.asana.com/0/1207817176293825/1208379852549386/f

This PR resolves an issue where persisted user tokens can prevent readers from logging in until the tokens expire (30 minutes) after logging out.

How to test the changes in this Pull Request:

1. As a reader without a password, log in via otp using the auth modal
2. Immediately sign out
3. Without reloading, attempt to sign in again
4. On epic/ras-acc you will get stuck at the first step of the auth modal. The continue button will cause the form to load for a second, then do nothing. On this branch, you should get another OTP email and be able to sign in again.
5. Smoke test some other paths for the auth flow to ensure nothing else has broken.

Other information:

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[miguelpeixe]

I wasn't able to reproduce the issue described in the PR while on the epic/ras-acc branch, but clearing the tokens on logout is a good practice.