SurfaceFlinger: Fix destruction of relatively Z-ordered layers.

We need to explicitly remove a layer from it's Z-order relative when
the layer is removed from compositing, and not rely on being the last
reference. In particular, at the time we are generating the list
of visible layers by traversing, any layer which had just been removed
will still be alive (but abandoned) with a ref in the previous list
of visible layers. So we will succeed in promotion, and copy it to the new
list. This way the layer achieves eternal life even after onRemoved is called.

Bug: 36693738
Test: Manual from BR
Change-Id: Ic6c3f64ceb0f603e7c0e51b136c23839858aa639