Use new modular temporary auth token constants in one-time login and password reset flows

Summary:
Ref T10603. This converts existing hard-codes to modular constants.

Also removes one small piece of code duplication.

Test Plan:

• Performed one-time logins.
• Performed a password reset.
• Verified temporary tokens were revoked properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10603

Differential Revision: https://secure.phabricator.com/D15476