Fixing a few more leaky refs to NavBarFragment/View

- Fix issue with fragment container attach listener always
  referencing the first fragment created for the display
- SysUI state callback needs to be unregistered for edge
  back gesture handler as well as it will be recreated

Bug: 160161606
Test: Trigger multiple config/overlay changes and ensure only
      one ref to NavBarFragment/View

Change-Id: I78973909d9714976516c1d2ebd77b9d01c52ba88