Removing default accessibility gesture handling.

1. The initial design was to have some accessibility gestures
   being handled by the system if the gesture handling access
   service does not consume the gesture. However, we are not
   sure what a good default is and once we add a default handler
   we cannot remove it since people may rely on it. Thus, we
   take the simples approach and let the accessibility service
   handle the gestures. If no gestures are handled the system
   will work in explore by touch as before.

bug:5932640

Change-Id: I865a83549fa03b0141d27ce9713e9b7bb45a57b4