Fix SingletonThreadLocal

Summary: it's really thread local at this point :)

Reviewed By: jmswen

Differential Revision: D2989668

fb-gh-sync-id: 423b9214922c92318181a62c583f58cd204b52e3
shipit-source-id: 423b9214922c92318181a62c583f58cd204b52e3

folly/SingletonThreadLocal.h

@@ -38,7 +38,6 @@ class SingletonThreadLocal {
 
   static T& get() {
 #ifdef FOLLY_TLS
-    *localPtr() = nullptr;
     if (UNLIKELY(*localPtr() == nullptr)) {
       *localPtr() = &(**SingletonT::get());
     }