Hi,
That error with jos_messages doesn't come from HikaShop or that custom field. It's an error of Joomla, and not related to HikaShop.
The problem is that this error is displayed on all the pages when you turn on the debug mode, so basically you can't use it in order to try to understand why the custom field doesn't work.
So it's normal that deleting the custom field doesn't resolve the error of the jos_messages table.
I would recommend to first fix your issue with that Joomla error before trying to look into the custom field issue since you can't use the debug mode at the moment. Note that in your message, you're talking about a jos_messages_cfg but the error you have is not on that table. It's on the jos_messages table. It's another table and you don't have it. That's why you have that error ! Normally you should have it on your database. Maybe because of a backup/restore issue you lost it or something like that.
You can add it back with the CREATE TABLE sql file of that table corresponding to your version of Joomla.