In the next diff, I'll add some code that will call logOut in this newly extracted callback. Instead of repeating it, I decided to extract it to a single place first.

This diff is a simple refactor. In addition to the following test plan I used for the next diff, I also made sure that Flow/ESLint were satisfied with the refactor.

• I hacked legacy-recover-keyserver-session.js to use the wrong password so the session recovery would fail
• I started the iOS simulator and logged in using a test user
• I opened the Redux Dev Tools
• I deleted the test user's cookie from the MariaDB database: DELETE FROM cookies WHERE user = 6390578 AND platform = 'ios'
• I sent a message as the test user
• I confirmed that session recovery was triggered in the Redux dev tools
• I confirmed that after session recovery failed, the user was logged out in the UI
• Via Redux dev tools, I confirmed that after session recovery failed, LOG_OUT_STARTED and LOG_OUT_SUCCESS were dispatched