Eliminate duplicate keys in pref xmls.

- Remove additional_system_update pref device_info page, we don't need
  it.
- Update keys in xml and Preference controller, and search index
  provider.
- Clean up in ScreenZoomPreference, it's anti-pattern to set fragment in
  constructor.
- Whitelist 2 that are super hard to remove.

Change-Id: Ibab6e2cb074513042a2ae007d9085aa64046eec8
Fixes: 67852637
Test: uniquePreferenceTest