Revert "Respect LayerSettings::alpha in Skia-RE for buffer layers"

This reverts commit 0559ca76.

Reason for revert: DroidMonitor: Potential culprit for b/174062136 - verifying through Forrest before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.

Change-Id: I7dbd7f9ff2c0abfcd2b200b35110727c143201dc