use new clearWallpaperLocked method everywhere

The old clear method had a lot of references. Replace these references
with a call to the new clear method. Now, everything that tries to clear
the wallpaper will call setWallpaperComponent(..) and not directly
bindWallpaperComponentLocked.

Flag: lockscreen lwp
Bug: 273443374
Test: atest WallpaperManagerTest
Change-Id: I2c7e8c3b4bcaf5a378e5f3b903075c422e2c432a