surfaceflinger: simplify TimeStats::getInstance

A static variable suffices.  And since TimeStats::getInstance is
always called, there is no need to put it on heap.

Test: boots
Change-Id: I954cfb18a6610f039b36c80946e32a7dc3a62a68
diff --git a/services/surfaceflinger/TimeStats/TimeStats.cpp b/services/surfaceflinger/TimeStats/TimeStats.cpp
index d77a324..0bc1c0a 100644
--- a/services/surfaceflinger/TimeStats/TimeStats.cpp
+++ b/services/surfaceflinger/TimeStats/TimeStats.cpp
@@ -32,11 +32,8 @@
 namespace android {
 
 TimeStats& TimeStats::getInstance() {
-    static std::unique_ptr<TimeStats> sInstance;
-    static std::once_flag sOnceFlag;
-
-    std::call_once(sOnceFlag, [] { sInstance.reset(new TimeStats); });
-    return *sInstance.get();
+    static TimeStats sInstance;
+    return sInstance;
 }
 
 void TimeStats::parseArgs(bool asProto, const Vector<String16>& args, size_t& index,