Fix race condition while WallpaperMS rebinding service.

Connection object could not receive onServiceConnected after
new process of the service was active.

How issue happen:
1. The process of wallpaper service died, AM schedule to restart,
WallpaperMS schedule to rebind.
2. WallpaperMS bind service with new connection object.
=> ActiveService bring up new process. Add this ServiceRecord to
   mPendingServices.
3. WallpaperMS unbind previous connection object.
=> ActiveService remove previous connection, also remove this
   ServiceRecord object from mPendingServices list.
4. Process ready, attach application but cannot find the service
   from pendingServices.

Solution: Do not remove the ServiceRecord object from mPendingServices
if there is any connection left.

Also use runnable object instead of method reference.

Bug: 148834472

Test: atest WallpaperManagerTest WallpaperManagerServiceTests
Change-Id: I3adec66de8ac0c7efc9ad3ffbf604b01eacb5720
Merged-In: I3adec66de8ac0c7efc9ad3ffbf604b01eacb5720
(cherry picked from commit d1551333)