Move the wallpaper title string from ThemePicker to WallpaperPicker2. am: 699bb63801 am: 6439e4210a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/11630521

Change-Id: I02e9afa309f34a1d3d1b98f31372959551b2d735