SF: Clean up constructors

This CL adds in-class member initializers and removes unused members.

Bug: 129433906
Test: Build
Change-Id: I24c264cc79f859536160472c765cb3911688f8c6
diff --git a/services/surfaceflinger/SurfaceTracing.h b/services/surfaceflinger/SurfaceTracing.h
index 4be2ee9..4773307 100644
--- a/services/surfaceflinger/SurfaceTracing.h
+++ b/services/surfaceflinger/SurfaceTracing.h
@@ -41,7 +41,7 @@
  */
 class SurfaceTracing {
 public:
-    SurfaceTracing(SurfaceFlinger& flinger);
+    explicit SurfaceTracing(SurfaceFlinger& flinger);
     void enable();
     bool disable();
     status_t writeToFile();