Reduce Beast dependencies by leveraging C++11 features:

* Remove beast::Atomic (RIPD-728):
  * Use std-provided alternatives
  * Eliminate atomic variables where possible

* Cleanup beast::Thread interface:
  * Use std::string instead of beast::String
  * Remove unused functions and parameters

* Remove unused code:
  * beast::ThreadLocalValue
  * beast::ServiceQueue

beast/module/core/thread/Workers.cpp

@@ -141,7 +141,7 @@ void Workers::deleteWorkers (LockFreeStack <Worker>& stack)
 
 //------------------------------------------------------------------------------
 
-Workers::Worker::Worker (Workers& workers, String const& threadName)
+Workers::Worker::Worker (Workers& workers, std::string const& threadName)
     : Thread (threadName)
     , m_workers (workers)
 {
@@ -232,7 +232,6 @@ void Workers::Worker::run ()
 class Workers_test : public unit_test::suite
 {
 public:
-
     struct TestCallback : Workers::Callback
     {
         explicit TestCallback (int count_)
@@ -251,13 +250,6 @@ public:
         std::atomic <int> count;
     };
 
-    template <class T1, class T2>
-    bool
-    expectEquals (T1 const& t1, T2 const& t2)
-    {
-        return expect (t1 == t2);
-    }
-
     void testThreads (int const threadCount)
     {
         testcase ("threadCount = " + std::to_string (threadCount));
@@ -276,14 +268,12 @@ public:
         // 10 seconds should be enough to finish on any system
         //
         bool signaled = cb.finished.wait (10 * 1000);
-
         expect (signaled, "timed out");
 
         w.pauseAllThreadsAndWait ();
 
-        int const count (cb.count.load ());
-
-        expectEquals (count, 0);
+        // We had better finished all our work!
+        expect (cb.count.load () == 0, "Did not complete task!");
     }
 
     void run ()