OSLO (Reuters) - Seadrill Chairman John Fredriksen will step down from his post with immediate effect, the company said on Thursday, while reporting third-quarter earnings that exceeded its own previous outlook.The 75-year-old billionaire investor, who is also Seadrill's top shareholder, said his support for the oil rig company remains unchanged. Fredriksen will be replaced by Glen Ole Roedland, who has worked in shipping, oil, gas and other industries, the company said.Oslo- and New..