Remove log_debug2 as well and simplify log.c.

tmux.c

@@ -70,7 +70,7 @@ logfile(const char *name)
 
 	if (debug_level > 0) {
 		xasprintf(&path, "tmux-%s-%ld.log", name, (long) getpid());
-		log_open(debug_level, path);
+		log_open(path);
 		free(path);
 	}
 }