Cleanup some incorrect / noisey calls to CustomContentCallbacks#onShow / onHide

-> In some instances, onResume would incorrectly call onShow
-> When pressing Home from CustomContent, we'd get a sequence of onHide,
   onShow, and then onHide due to some deferred actions in onNewIntent.
   Got rid of the onShow.

issue 17629011

Change-Id: I9b4f2ef682f5a7060e68210866fa05452076e428