Make Email GeneralPreferences subclass GeneralPrefsFragment.
Only contains a minimum of code to strip out archive-related prefs,
which are not relevant to the current state of Email back-ends.
(These actions could be relevant for Gmail IMAP extensions if support is added for them)
b/9566150
Change-Id: Ie8e26379ed504c7d96c2a2f8e1c843bbe0582cc7