By Jeff Mason and Doina Chiacu WASHINGTON (Reuters) -President Joe Biden took steps to overhaul U.S. policy on marijuana on Thursday by pardoning thousands of people with federal offenses for simple marijuana possession and initiating a review of how the drug is classified. Biden said thousands of people with prior federal convictions could be denied employment, housing or educational opportunities and his executive action would relieve such “collateral” consequences. Nearly 40 U.S. states have legalized marijuana use in some form, but it remains completely illegal in some states and at the fe…