I didn't mind it, even if it was an info-dump. It was an engaging way to get across that information about the dragon skulls, hammer in the point that dragons no longer exist, and flesh out Viserys' character even more than the books ever care to.
My only complaint with that scene was it went on a hair too long. Probably could've dropped out all the name-dropping of past dragons, considering it's not important, and likely confuses non-readers. I loved the sudden about-turn Viserys had when he believed Doreah was overstepping her bounds as a slave.
The Sansa/Mordane scene I thought was completely unnecessary though. The way they just turned it into a history lesson seemed way too forced, as if the Septa were speaking to the audience, not Sansa.