surfaceflinger: remove BufferLayerConsumer::mUseFenceSync

BufferLayerConsumer::mUseFenceSync is always false.  As a result, we
can remove EGLSyncKHR from EglSlot and PendingRelease.

Test: boots
Change-Id: I0fec2137a6548335303e990232637b2da00fa3c6
4 files changed