By Dawn Chmielewski and Hyunjoo Jin (Reuters) -Elon Musk avoided discussing the collapsed Twitter deal as he addressed an audience of moguls on Saturday in Sun Valley, two sources who attended the conference told Reuters. In a wide-reaching interview, Musk spent most of his time talking about colonizing Mars and extolling the virtues of boosting birth rates on Earth, said the sources. Musk, chief executive of Tesla Inc and rocket company Space X, has long advocated establishing a civilization on the red planet. Musk earlier this week said he will do his best to help what he called “the underpo…