Update log_msg.h

include/spdlog/details/log_msg.h

@@ -32,8 +32,7 @@ struct log_msg
     }
 
     log_msg(const log_msg &other) = default;
-    log_msg(log_msg &&other) = default;
+    log_msg &operator=(const log_msg &other) = default;
-    log_msg &operator=(log_msg &&other) = default;
 
     const std::string *logger_name{nullptr};
     level::level_enum level{level::off};