Liver is an important part of a dog's diet. If you were feeding a homemade diet, I would tell you to be careful to give the right ratio because it's true that you shouldn't overdo it (generally it makes up about 5% of the dogs diet when feeding raw). But the pre-made foods you're feeding are already balanced with the right ratio of everything. Plus, Acana and Orijen are trustworthy high quality brands.
Unless you feed a huge amount of liver treats every day, I doubt you're overdoing it. Liver is quite rich and often leads to loose stools if you give too much so that's one way to tell.
But if you're still worried, there are plenty of other good treats that don't have liver in them.