Clean up PreviewFragment and its child classes (Part 2) am: fe3a5d42b9 am: 295ac31588

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/WallpaperPicker2/+/11636057

Change-Id: I900d35e8598b24f761fc72bd749db5e2be491a50