Rearrange PIA themes.

All activities require no action bar and title since only a dialog is
shown. As such, we dont need to specify a theme for each individual
activity. We can include the `NoActionBar` theme's properties into the
application theme.

Test: Manual. Install an APK and observe the UI
Bug: 316810746

Change-Id: I0f420793edfee54c8ac352456f06d610b75458c8