Removes unused JSON logger.

References:
- https://github.com/Project-OSRM/osrm-backend/pull/2769

include/engine/routing_algorithms/map_matching.hpp

@@ -9,7 +9,6 @@
 
 #include "util/coordinate_calculation.hpp"
 #include "util/for_each_pair.hpp"
-#include "util/json_logger.hpp"
 
 #include <cstddef>
 

include/util/json_logger.hpp

@@ -1,62 +0,0 @@
-#ifndef JSON_LOGGER_HPP
-#define JSON_LOGGER_HPP
-
-#include "osrm/json_container.hpp"
-
-#include <boost/thread/tss.hpp>
-
-#include <string>
-#include <unordered_map>
-
-namespace osrm
-{
-namespace util
-{
-namespace json
-{
-
-// Used to append additional debugging information to the JSON response in a
-// thread safe manner.
-class Logger
-{
-    using MapT = std::unordered_map<std::string, Value>;
-
-  public:
-    static Logger *get()
-    {
-        static Logger logger;
-
-        bool return_logger = true;
-#ifdef NDEBUG
-        return_logger = false;
-#endif
-#ifdef ENABLE_JSON_LOGGING
-        return_logger = true;
-#endif
-
-        if (return_logger)
-        {
-            return &logger;
-        }
-
-        return nullptr;
-    }
-
-    void initialize(const std::string &name)
-    {
-        if (!map.get())
-        {
-            map.reset(new MapT());
-        }
-        (*map)[name] = Object();
-    }
-
-    void render(const std::string &name, Object &obj) const { obj.values["debug"] = map->at(name); }
-
-    boost::thread_specific_ptr<MapT> map;
-};
-}
-}
-}
-
-#endif /* JSON_LOGGER_HPP */