SF: detachLayer from Client earlier on destruction

- When a Layer is destroyed the Layer destructor isn't called until
  the next vsync refresh. However, the onRemoved() callback is called
  on the next invalidate. So it's possible to submit a transaction on
  the layer in between the call to onRemoved() and the destructor
  being called.
- Call detachLayer() from onRemoved() instead of from the destructor
  so that any transactions on a destroyed Layer will fail to get the
  Layer object even if the destructor has yet to be called.

Bug 25887783

Change-Id: Ic2371f695bc91aa7120bf6506bb834ceb536420e