Cleanup the AppbarFragment usage in PreviewFragment

Cleanup only, no business logic change

- AppbarFragment had a good pattern to set title on toolbar. PreviewFragment won't do it throught accessing activity tool bar.
- AppbarFragment had a good pattern to set bottom action bar, which is widely used within the app, PreviewFragment won't do it by itself.

Test: Manually
Fixes: 160211359
Change-Id: Ie9e390c69e82d02192af0e2bcc5274b9a64d514c