I deleted my standard deck, even remade it and I am still getting this error. The only change I made was adding in the golden dragon from the tavern brawl this week.
Unfortunately, this is a double award visual glitch. You only get one of each Golden card.
The bug is that the Card Collection shows two awards of Golden Bronze Herald or Golden Recurring Villain.
The workaround is to restart Hearthstone.
This has been reported and in future when you do find a game bug: