THRIFT-2607 ThreadManager.cpp warning on clang++ 3.4

Patch: Konrad Grochowski
diff --git a/lib/cpp/src/thrift/concurrency/ThreadManager.cpp b/lib/cpp/src/thrift/concurrency/ThreadManager.cpp
index f2c0fa5..1f897ba 100644
--- a/lib/cpp/src/thrift/concurrency/ThreadManager.cpp
+++ b/lib/cpp/src/thrift/concurrency/ThreadManager.cpp
@@ -553,8 +553,7 @@
  public:
   SimpleThreadManager(size_t workerCount=4, size_t pendingTaskCountMax=0) :
     workerCount_(workerCount),
-    pendingTaskCountMax_(pendingTaskCountMax),
-    firstTime_(true) {
+    pendingTaskCountMax_(pendingTaskCountMax) {
   }
 
   void start() {
@@ -566,7 +565,6 @@
  private:
   const size_t workerCount_;
   const size_t pendingTaskCountMax_;
-  bool firstTime_;
   Monitor monitor_;
 };