Removed redundant "using log_thread_id=size_t"

include/spdlog/details/log_msg.h

@@ -90,7 +90,7 @@ struct log_msg
     std::string logger_name;
     level::level_enum level;
     log_clock::time_point time;
-    log_thread_id thread_id;
+    size_t thread_id;
     fmt::MemoryWriter raw;
     fmt::MemoryWriter formatted;
 };