This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
Changes to functionality
- Removed syncing of user metadata including gender, location etc.
These are no longer available to standard Facebook applications.
- Removed the remote 'revoke' functionality. No other providers have
it, and it does not appear to be standard practice in other apps.
- The 'facebook_no_email' event is no longer logged. The system can
cope fine with a missing email address.
Data is migrated to the new user_associated_accounts table.
facebook_user_infos can be dropped once we are confident the data has
been migrated successfully.
