Remove custom scrollbar logic

 Bug: 6505722
 When we scroll the base layer we do so by calling scrollTo on the view,
 which handles all the scrollbar logic for us. Remove the custom keep alive
 code which floods the handler queue, as well as remove the unnecessary
 invalidate and awakenScrollbar calls (View does that for us)

Change-Id: Ia2503c549a22ec71d99295fe62b676fecc367ea3