Remove unused member from backtracer

include/spdlog/details/backtracer.h

@@ -17,25 +17,15 @@ namespace details {
 class backtracer
 {
     std::mutex mutex_;    
-    size_t n_messages_;
     circular_q<log_msg_buffer> messages_;
 
 public:
-    explicit backtracer(size_t n_messages)
-        : n_messages_{n_messages}
-        , messages_{n_messages}
+    explicit backtracer(size_t n_messages) : messages_{n_messages}
     {}
 
-    backtracer(const backtracer &other)
-        : n_messages_{other.n_messages_}
-        , messages_{other.messages_}
+    backtracer(const backtracer &other) : messages_{other.messages_}
     {}
   
-    size_t n_messages() const
-    {
-        return n_messages_;
-    }
-
     void add(const log_msg &msg)
     {
         std::lock_guard<std::mutex> lock{mutex_};