By Tiyashi Datta and Sheila Dang (Reuters) -Elon Musk accused Apple Inc of threatening to block Twitter Inc from its app store without saying why in a series of tweets on Monday that also said the iPhone maker had stopped advertising on the social media platform. The billionaire CEO of Twitter and Tesla also said Apple was pressuring Twitter over content moderation demands. The action, unconfirmed by Apple, would not be unusual as the company has routinely enforced its rules that led to the removal of apps such as Gab and Parler, which is popular with U.S. conservatives. Parler was restored by…