http: Remove numThreads and ThreadCounter

The HTTP worker thread counter, as well as the RAII object that was used
to maintain it, is unused now, so can be removed.

Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>

zcash: cherry picked from commit 11e0151
zcash: bitcoin/bitcoin#12366

src/httpserver.cpp

@@ -73,30 +73,10 @@ class WorkQueue
     std::deque<std::unique_ptr<WorkItem>> queue;
     bool running;
     size_t maxDepth;
-    int numThreads;
-
-    /** RAII object to keep track of number of running worker threads */
-    class ThreadCounter
-    {
-    public:
-        WorkQueue &wq;
-        ThreadCounter(WorkQueue &w): wq(w)
-        {
-            std::lock_guard<std::mutex> lock(wq.cs);
-            wq.numThreads += 1;
-        }
-        ~ThreadCounter()
-        {
-            std::lock_guard<std::mutex> lock(wq.cs);
-            wq.numThreads -= 1;
-            wq.cond.notify_all();
-        }
-    };
 
 public:
     WorkQueue(size_t maxDepth) : running(true),
-                                 maxDepth(maxDepth),
-                                 numThreads(0)
+                                 maxDepth(maxDepth)
     {
     }
     /** Precondition: worker threads have all stopped (they have been joined).
@@ -118,7 +98,6 @@ class WorkQueue
     /** Thread function */
     void Run()
     {
-        ThreadCounter count(*this);
         while (true) {
             std::unique_ptr<WorkItem> i;
             {