core, api: remove unneeded cast to time_t

The field `tv_sec` of struct timeval is already time_t, the cast is not needed.

src/plugins/plugin-api-info.c

@@ -1042,7 +1042,7 @@ plugin_api_info_uptime_current_cb (const void *pointer, void *data,
     (void) info_name;
 
     return plugin_api_info_build_uptime (
-        (time_t)weechat_current_start_timeval.tv_sec,
+        weechat_current_start_timeval.tv_sec,
         arguments);
 }