LineageParts: update for Style APIs updates

- The app that has set the current global style will be
  displayed in the global style preference (unless it was set from
  LineageParts itself).
- Accents list is now built using the API's getTrustedOverlays() method
- Also cleanup unused code

Change-Id: Ib7b1ca978635e568f7f0c147407270e5f588f0f1
Signed-off-by: Joey <joey@lineageos.org>