Restart accessibility services after they update.

In ag/1273924, we stopped restarting services that were
still bound. When the package changes, however, the system
unbinds from a service and has no way to tell us that it is
not going to restart it (as it would if the service
crashed.)

Now we listen for package updates and unbind affected
services. The services will then be restarted as there will
be enabled services that are no longer bound.

Bug: 30866905
Change-Id: I375edfd6a37ed25f959ec354930cec8f288deb6b