Do not include Boost.Thread is a sub-header is good enough.

`boost::thread_specific_ptr` lives in `<boost/thread/tss.hpp>`.

In addition, fix the includes in the touched header.

Reference:

- http://www.boost.org/doc/libs/1_59_0/doc/html/thread/thread_local_storage.html

util/json_logger.hpp

@@ -30,7 +30,10 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <osrm/json_container.hpp>
 
-#include <boost/thread.hpp>
+#include <boost/thread/tss.hpp>
+
+#include <string>
+#include <unordered_map>
 
 namespace osrm
 {