SurfaceFlinger: Remove removeLayer

We remove explicit layer destruction and replace it
with reparent->null, completing the transition to
a reference counted model.

Test: Manual
Bug: 62536731
Bug: 111373437
Bug: 111297488

Change-Id: I8ac7c5c5125e1c8daf84b42db00e1dd93a544bb5
15 files changed