use faster impl in Singleton stack traces

Summary: It's already not async-signal-safe so just use the fast version of getting the unsymbolized stack traces.

Reviewed By: chadaustin

Differential Revision: D29439597

fbshipit-source-id: 5a727d6a1c37a1c29bce84d866bf4863774c5ff1

folly/detail/SingletonStackTrace.cpp

@@ -31,7 +31,7 @@ std::string getSingletonStackTrace() {
   auto addresses =
       std::make_unique<symbolizer::FrameArray<kMaxStackTraceDepth>>();
 
-  if (!getStackTraceSafe(*addresses)) {
+  if (!getStackTrace(*addresses)) {
     return "";
   } else {
     symbolizer::ElfCache elfCache;