Changes Hub quick picker to get current wallpaper from preferences

This also fixes the picker crash when no recent wallpapers were
available, and removes some dead code that was causing compile errors.

Fixes: 270980607
Bug: 270997324
Test: Manually verified picker behavior for Hub and pre-Hub flows
Change-Id: Id504f6a7162f8834cc5f57c20adc3007a4115435