Use Layer IDs instead of handles in BufferCountTracker

Allows more versatility in looking up buffer counts by
layer ID. Layer handles will not always be available for
lookup.

Test: presubmit
Bug: b/294922229
Flag: EXEMPT pure refactoring
Change-Id: Ifba8b19f24f3f3cf35d247490a17fe3b8c4920e0
diff --git a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
index 9dae06a..7a12f65 100644
--- a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
+++ b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
@@ -635,7 +635,7 @@
     void destroyAllLayerHandles() {
         ftl::FakeGuard guard(kMainThreadContext);
         for (auto [layerId, legacyLayer] : mFlinger->mLegacyLayers) {
-            mFlinger->onHandleDestroyed(nullptr, legacyLayer, layerId);
+            mFlinger->onHandleDestroyed(legacyLayer, layerId);
         }
     }