Accessibility services that do not accept events are mismanaged.

1. If an accessibility service does not specify that it handles any
   event types it was never added to the list of services while
   the system is bound to it. Since the service is not in the list
   with enabled services we never unbind it, hence it consumes
   resources without doing nothing. This is also semantically
   incorrect because a sevice may not want to receive events while
   handling only gestures.

bug:5648345

Change-Id: Id478a4704cdeeb1729330f6ae4b8ff9e06320952