Remove the accessibility focus search code.

1. In JellyBean we have added some APIs to search for next accessibility
   focus in various directions and set accessibility focus from hover.
   However, we have decided that there is not clean answer for how this
   should behave and the APIs were hidden. Now the accessibility service
  is responsible for that. The unused code is now taken out.

2. This patch also takes out the hidden attribute accessibiligyFocusable
   since we moved the responsibility for implementing focus search strategy
   to accessibility services and we did not need that for Jellybean which
   is a good sign that this is not needed. I general this is one less thing
   for an app developer to worry about. We can add this if needed later.

bug:6773816

Change-Id: I0c858d72c93a2b7ff1f8f35a08d33ec4b9eb85fd