Extract will contain enough minerals to give the yeast what they need, so no salt additions are necessary. However, if you really want a minerally profile like burton on trent style beers, you'll need some mineral additions. Mainly gypsum, which will accentuate the hop bitterness. I would say try the recipe without additions and it should end up being a good beer. Then if you decide its lacking some characteristic of a bitter, you may want to research water salts that would be appropriate for addition to your boil for the extract version of the beer.
Short answer, no you don't need salt additions for an extract beer.