Remove possible residual callbacks when detach wallpaper.

Lower the chance for continuously bind same wallpaper service from
tryToRebind and package update.
No matter which one of them calls bind wallpaper first, as long as
the bind sequence success, there will create a new wallpaper
connection then detach previous one, at that time we should remove
those possible residue callbacks on previous connection to make sure
the connection is removed completely.

Bug: 160279563
Test: atest WallpaperManagerTest WallpaperManagerServiceTests
MultiDisplaySystemDecorationTests

Change-Id: I4507b4aa5449ab960fb72dceddfcd83e4ae0a8bb