(CE-1185) Fix fatal error on close account

When the new FacebookClient is enabled, the old FBConnect isn't available
and so removing the account from FBConnect fails. Add a check for the new
version and use its method of disconnecting accounts from Facebook.

This has stopped account closures from being logged since the start of the month.

Cherry-picked from dev (https://github.com/Wikia/app/pull/5830).

For approval by UConn before releasing. /cc @garthwebb @lizlux