Clean up uses of refreshStartTime for stats.

refreshStartTime is keeps track of frame refreshes for
stats and can be set from SurfaceFlinger. This makes
subsequent changes in refactoring
SurfaceFlinger#composite cleaner and makes tracking the
metric more consistent between changes.

The refreshStartTime field can be removed entirely from
LayerFE's CompositionResult and removed as an argument
in LayerFE#onPreComposition.

Bug: b/294936197, b/329275965
Test: presubmit
Change-Id: I97988315f8982d05aec4b2684d4f5f1826a0fefa
diff --git a/services/surfaceflinger/LayerFE.cpp b/services/surfaceflinger/LayerFE.cpp
index 2dbcb84..43a4397 100644
--- a/services/surfaceflinger/LayerFE.cpp
+++ b/services/surfaceflinger/LayerFE.cpp
@@ -82,8 +82,7 @@
     return mSnapshot.get();
 }
 
-bool LayerFE::onPreComposition(nsecs_t refreshStartTime, bool) {
-    mCompositionResult.refreshStartTime = refreshStartTime;
+bool LayerFE::onPreComposition(bool) {
     return mSnapshot->hasReadyFrame;
 }