Get rid of the field WallpaperData.mSupportsMultCrop

There are no short term plans to crop live wallpapers on the window
levels. Let's not keep confusing and unnecessary logic. If one day we
decide to use multi-crop for a live wallpaper, we'll rewrite something
similar.

Flag: ACONFIG com.android.window.flags.multi_crop TEAMFOOD
Bug: 330518320
Test: atest WallpaperManagerTest
Change-Id: I46e8469593303a77012e28e6019c6d789041cfd1